Analysis of Variance
Analysis of variance revealed significant differences among genotypes for all the characters studied at both 5% and 1% level except for zinc content which is significant at 5% level only (Table 1). Similar reports of significance for ANOVA were given for yield and quality traits in groundnut by Shankar et al. (2019) and Chandrasekhara et al. (2020). Presence of high phenotypic variability is important for the traits under a study, to identify genomic/functional variations if any at the targeted traits and thereby to tag a trait at molecular level.
Table 1
Analysis of variance for yield and seed quality traits in groundnut
S. No | Character | Mean Sum of Squares |
Replications (df: 2) | Treatments (df : 23) | Error (df : 46) | |
1 | Plant Height (cm) | 133.08 | 298.827** | 27.71 | |
2 | Primary Branches per Plant (No.) | 2.94 | 4.243** | 0.56 | |
3 | Secondary Branches per Plant (No.) | 0.13 | 2.660** | 0.08 | |
4 | Pod Yield per Plant (g) | 4.97 | 30.948** | 5.04 | |
5 | Hundred Pod Weight (g) | 285.89 | 1329.038** | 217.79 | |
6 | Hundred Kernel Weight (g) | 36.15 | 144.416** | 15.12 | |
7 | Shelling Percentage (%) | 12.26 | 83.413** | 16.33 | |
8 | Oil Content (%) | 0.49 | 1.708** | 0.06 | |
9 | Protein Content (%) | 0.06 | 0.282** | 0.07 | |
10 | Total Free Aminoacids (TFA)(µg/g) | 6.31 | 22218.767** | 64.76 | |
11 | Total Soluble Sugars (TSS)(g/g) | 0.02 | 0.062** | 0.00 | |
12 | Total Sucrose Content(µg/g) | 1.38 | 264.623** | 2.91 | |
13 | Fe Content (ppm) | 134.11 | 4359.679** | 357.81 | |
14 | Zn Content (ppm) | 48.76 | 194.429* | 91.88 | |
*,** significant at 5% and 1% level respectively |
Standardization Of Markers With Rice
All the 45 markers that are targeted to 24 rice yield and quality trait governing genes selected for genotyping analysis were standardized primarily with rice genomic DNA of NLR34449 at various temperatures (temperature gradient) i.e. 50–65°C (Supplementary Fig. 1). Of 45 markers, 41 primers representing all 24 genes were amplified with NLR 34449(Table 2), four primers namely MOC1, ex Gn1a, exDep1 and C62 were not amplified with NLR 34449. The primers that amplified with rice were further tested for their transferability with groundnut genotypes.
Table 2
Exploitation of 45 rice gene tagged markers in the study and their allele sizes observed in groundnut with respect to rice
Trait reported in rice/considered to be studied in groundnut | Gene Name | Chr | Marker | Annealing temperature | SIZE OF ALLELE (bp) |
Reported size of allele in Rice | Observed size (bp) |
Rice | wild groundnut | cultivated groundnut |
Plant height | sd1 | 1 | sd1-h | 55 | 843 (semidwarf-Habataki); 800 (normal plant introduced with sd1- Sashaniki) | 843 | 190 | NA |
Plant Architecture | MOC1 | 6 | MOC1 | 65** | 1900(primer blast reference) | NA | NA | NA |
| OsSPL14 | 8 | OsSPL14 | 50 | 500 (Heavy panicle) | 500 | 500 | 500 |
| Plant Architecture and Yield 1 (PAY1) | 8 | PAY1sp6 | 53 | 200 (Nipponbare)-primer blast reference | 200 | 200 | 200 |
Yield Contributing Genes | Gn1a | 1 | ex Gn1a | 50–65** | 532(Habataki, ST12)-donor for MAB &highgrain number per panicle, 321bp(Parao) | NA | NA | NA |
| Grain Number2 (GN2) | 2 | RM3535 | 58 | 185 | 185 | 185 | 185 |
| YLD | 8 | RM223 | 58 | 139–163 (identify aromatic and non-aromatic germplasm) | 165 | 165 | 165 |
| | | HY2-4 | 50–65 | | 900 | NA | NA |
| NAL1/SPIKELET NUMBER (SPIKE) | 8 | SPIKE-INDEL 3 | 62 | 151(CT805,Parao)-yield positive, NAL1- japonica allele,171 | 171 | 171 | 171 |
| EP3 | 2 | S5 803 | 59 | 243 (erect panicle) | 243 | NA | NA |
| Hybrid sterility LOC_Os06g11010 | 6 | S5-1 | 59 | 321(02428) -wide compatibility var (heterosis and ideal plant type breeding),457(Nipponbare) - incompatible var | 457 | NA | NA |
| SCM2/Aberrant Panicle Organization 1 (APO1) | 6 | SCM2-INDEL1 | 57 | 117 (Habataki)- high yield and lodging resistance, 105 (Parao) | 117 | 117 | 117 |
| DEP1 (DENSE AND ERECT PANICLE), | 9 | exDep1 | 50–65** | NA | NA | NA |
| | | DEP1 INDEL1 | 58 | 1031 (increased grain number per panicle), 406(Osmanick-Turkish high yielding variety) | 1031 | NA | NA |
| | | DEP1-1 | 58 | 1235(Wuyunjing8) (erect panicle) --heterosis and ideal plant type breeding,1860(Nipponbare)-non-erect panicle | 1860 | NA | NA |
| | | Dep1s7 | 59 | 127(primer blast reference) | 127 | 127 | 127 |
Seed Quality Genes | GS2 | 2 | RM3212 | 58 | 181(Nipponbare)- medium grain phenotype | 181 | 181 | 181 |
| GS3 | 3 | RGS1 | 55 | 180 (Improve Grain Size),200 | 180 | 180 | 180 |
| | | SR17 | 58 | 1000 (Improve Grain Size),1400 | 1400 | NA | NA |
| GS5 | 5 | C62 | 50–65** | NA | NA | NA |
| | | RM593 | 58 | 279(primer blast reference) | 279 | NA | NA |
| | | GS5 INDEL1 | 55 | 67(ST6, Parao)- wide grain, 63 (NSIC Rc158)- medium grain | 63 | 63 | 63 |
| | | RM574 | 58 | 240(Zhenshan97) (Oryza sativa var.indica) - grain width | 240 | 240 | 240 |
| OsSNB, SUI4/SNB | 7 | OsSNB2 | 58 | 997(primer blast reference) | 50 | 50 | 50 |
| GW2 (Grain weight) | 2 | GW2SNP2 | 58 | 51(Kasalath), TD70-31&21bp fragments- more valuable for grain width and weight | 51 | 51 | 51 |
| | | GW004 | 57 | 750,1050- not much used for detecting allelic variations in GW2 | 750 | NA | NA |
| GW5 /SW5 | 5 | RM3328 | 57 | 119(increase grain width) | 119 | NA | 95 |
| | | RMw513 | 59 | 171(Nipponbare)- slender grain and low chalkiness | 600 | 700 | 600 |
| | | N1212 | 59 | 759 (increased grain width) - Nipponbare, TD70 | 65 | 65 | 65 |
| GW7 | 7 | RM22015 | 58 | 176(1000 grain weight) | 176 | 176 | 176 |
| GLW7/OsSPL13 | 7 | GLW7/OsSPL13/SPL13 | 62 | 140(primer blast reference) | 140 | 140 | 140 |
| | | RM505 | 55 | 220(Sonasal) -short grain, 170(Chiguhong)-grain plumpiness,180(PB1121) -extra-long sender grain | 500, 180 | NA | 400 |
| | | RM21945 | 55 | 292 | 292 | 292 | 292 |
| GW8 | 8 | GW8 PRO2 | 58 | 861(primer blast reference) | 861 | NA | 861 |
Shelling Percentage | GIF1 | 4 | exGIF1 | 58 | 96(primer blast reference) | 96 | 96 | 96 |
| | | RM16942 | 58 | 181 | 181 | NA | 135 |
Flowering Time | Hd1 | 6 | Hd1 | 50 | 1886,1850(primer blast reference) | 100 | 100 | 100 |
| | 6 | Hd1 AGC | 65 | 441 (BL1Sakha101)-moderate heading, 490 (Giza171) -late heading, 620 (Giza177, Sakha 103) -early heading date | 140 | 140 | 140 |
| Hd3a | 6 | Hd3a | 62 | 1108,2163(primer blast reference) | 90 | 90 | 90 |
| Hd5/DTH8 | 8 | DTH8-INDEL | 57 | 121 (primer blast reference) | 480 | 70 | 140 |
Seed Micronutrient Content | YSL2 | 2 | vf0226164188 | 62 | 137 | 137 | 200, 300 | 137 |
| | | vf0226169288 | 62 | 300 | 300 | NA | NA |
| | | vf0226164382 | 65 | 157 | 157 | NA | NA |
| YSL15 | 2 | 02g43410 | 55 | 486 | 486 | NA | 310 |
| YSL13 | 4 | 04g44300 | 55 | 223 | 223 | NA | NA |
Standardization Of Selected Markers With Peanut Genotypes
The 41 markers that showed amplification with rice were standardized with both wild groundnut genotypes (Arachis glabrataand Arachis villosa) and with three cultivated groundnut varieties viz., Dharani, TPT 3 and ICGV 00350 initially, to observe the amplification in peanut (Supplementary Fig. 2). Out of 41 amplified rice markers, 31 (76%) showed amplification with cultivated groundnut genotypes, except sd1-h marker, that amplified only with wild groundnut genotypes. However, 25 showed amplification with diploid wild groundnut except RM3328, GW8PRO2, RM505, RM16942 and YSL15 markers, which are amplified with cultivated groundnut (Table 3).A total of ten markers viz., s5-803, s5-1, HY2-4, Dep1indel1, Dep1-1, SR17, RM593, GW004, YSL13 and YSL2 showed amplification, only with rice.
Table 3
Overview of the markers used in the study and their amplification status
Crop | Rice yield markers | Groundnut oil quality markers | Mungbean Bruchid tolerance | Total markers | % Amplification across genomes |
| Markers screened (genes targeted) | Marker amplified | Markers screened (genes targeted) | Markers amplified | Markers screened (gene number) | Amplification status | Markers used | Amplified |
rice | 45 (24) | 41 (91%) | 4(2) | 3 (75%) | 1(1) | Not amplified | 50 | 44 | 88 |
Ground nut | 41 | 31 (76%) | 4 | 4 (100%) | 1 | 1 | 46 | 36 | 78 |
Cross Transferability Of Markers Between Rice And Peanut
During the course of crop evolution, the genome content across plant kingdom is proved to be conserved and is evident from many synteny studies across genera/families. Further, conservation of functional genes and important motifs are reported by many earlier research groups (Trivedi et al., 2013; Hussien et al., 2014). The transferability was analysed with similar allele sizes of groundnut genotypes to rice i.e. which are observed across the genotypes under study.
Plant Height
Plant height is screened with sd1-h marker ofsd1gene, which is responsible for dwarf stature of the plant that encodes gibberellin 20-oxidase (GA20ox-2). This gibberellin 20-oxidasehelps to prevent severe dwarfism in sd-1mutants. Habataki rice variety expressed 843bp of allele size for semi-dwarfism, whereas Sashaniki expressed 800bp size for tallness in rice. In the current study, this marker showed amplification of 843bp in rice only (as in Monna et al., 2002) and 190bp product size in wild peanut, whereas cultivated peanut didn’t show any amplification. Thus, it might be due to the massive changes happened at the primer locus or may be due to the complete loss of respective alleles/gene while evolution.
Plant Architecture
OsSPL14 (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 14), also known as WEALTHY FARMER'S PANICLE/IDEAL PLANT ARCHITECTURE 1 is regulated by a microRNA, OsmiR156. Increase in level of transcript of OsSPL14 increases grain productivity and also ideal plant architecture (IPA) phenotype (Miura et al., 2010) in rice. This marker amplified 500bp allele size in 11 groundnut genotypes i.e. similar to rice allele, (Fig. 2) except in Narayani, Kalahasti, Prasuna, Rohini, Bheema, Dharani and Nithya Haritha, which amplified 70bp allele size. However, Greeshma showed 390bp allele upon amplification. OsSPL14 functions for heavy panicle with lot of secondary branches and also it promotes ideal plant type in rice(Mohapatra et al., 2018). In groundnut secondary branch number is a major yield governing trait. Thus, characterizing of this gene in peanut might help in improving yield potential by altering the branching and flowering/pod formation pattern.
PLANT ARCHITECTURE AND YIELD 1 (PAY1) gene improves plant architecture and grain yield. The tagged marker, PAY1SP6 was used to identify the transferability from rice to peanut. Interestingly, it was observed an allele of 200bp in rice and both wild and cultivated peanut genotypes (Fig. 2). Zhao et al. (2015) in their study, selected a wildrice introgression line YIL55, which displays short plant height, high tillering, thin stems, fewer grains and low yield and a mutant with modified plant architecture called PAY1. When compared, PAY1 exhibited greater plant height, lower tiller number, smaller tiller angle, thicker stems and larger panicles due to the presence of longer internodes, more vascular bundles in stems, and production of more secondary branches. NILs in Teqing or 9311 genetic background also demonstrated that PAY1 could shape better plant architecture and enhance grain yield of rice which reveals that PAY1 is a dominant regulator of plant architecture. Hence, characterization of these kinds of genes can help better in shaping the groundnut pant along with production of more number of reproductive units.
Yield Contributing Genes
Grain number ( GN2 ) which functions as OsWAK (Wall-Associated Kinase) receptor like-protein is responsible for increase in grain number. The marker, RM3535 (Rice Microsatellite) which is closely tagged to GN2 gene was selected for study. This marker amplified 185bp in all the genotypes of peanut which is in accordance with rice. Sequencing of this allele can further strengthen its conformity and to use the allelic variants in groundnut improvement breeding (Fig. 2).
The YLD (yield) gene linked SSR marker RM223 amplified 165bp in all genotypes of rice and peanut (Fig. 2). This marker also has tagged to aromatic/non-aromatic trait of rice as reported in Jewel et al. (2011).
SPIKELET NUMBER ( SPIKE ) is allelic to Narrow Leaf1 (NAL1) that encodes a plant-specific protein with an unknown biochemical function. SPIKE-INDEL3 marker of SPIKE gene amplified 171bp in rice, which can increase spikelet number, as reported by Kimetal.(2016). In groundnut also the 171bp allele was observed i.e. similar to rice. However, the marker showed non-specific amplification of 250bp fragment along with 171bp among cultivated peanut genotypes (Fig. 2).Erect panicle 3 (EP3) encodes a putative F-box protein and is associated with erect panicle. S5-803 marker expressed 243bp allele size only in rice as described in Piao et al., 2009 (Supplementary Fig. 1).
SCM2/ABERRANT PANICLE ORGANIZATION 1 ( APO1 ) encodes an F-box-containing protein which is involved in controlling rachis branching in panicle, tiller outgrowth, and culm diameter. SCM2 (STRONG CULM2) is a mild allele of APO1 found in Habataki variety and showed increased culm diameter and grain number per panicle without a reduction in tiller number. This SCM2-Habataki allele is regarded as a useful allele of APO1 gene for increasing yield and lodging resistance in breeding programs(Kim et al., 2016). In the current study, SCM2 INDEL1 marker amplified at 117bp in all genotypes of rice and peanut. However, the amplification intensity in peanut is low compared to rice. This can be implied to the presence of similar gene in groundnut with changes happened at the primer annealing site. Therefore, designing of primers for other parts of the gene can justify the presence of SCM2 ortholog in groundnut, strongly.
DENSE AND ERECT PANICLE 1( DEP1 ) which encodes phosphatidyl ethanolamine binding protien (PEBP) was selected which is responsible for three different traits such as dense panicle, high grain number per panicle and erect panicle. Gain of function mutation in DEP1 showed increased number of primary and secondary branches and also grain number per panicle. DEP1 also controls number of panicle branches through cytokinins because expression level of OsCKX2’s down-regulation (Huang et al., 2009). Four markers viz., exDEP1, DEP1INDEL1, Dep1s7, DEP1-1 were used for genotyping analysis of groundnut. Of these markers, exDEP1 didn’t show amplification with any genotypes. DEP1INDEL1 and DEP1-1 produced amplicons of 1030bp (as in Kim et al., 2016) and 1860bp which indicates non-erect panicle type (as in Li et al., 2017), respectively in only rice genotypes (Supplementary Fig. 4) and no amplification was seen in peanut genotypes. The marker Dep1s7 expressed 127bp allele size in rice and all peanut genotypes i.e. both wild and cultivated by which study of this gene ortholog is possible from rice to peanut in order to identify pod number increase per plant(Fig. 2).
Seed Quality Genes (Seed Size And Weight)
Seed size genes of rice were utilized to found orthologs in other cereals. Thus the current study proceeded to found peanut orthologs with the following seed size governing genes of rice.
GS2 (Grain Size) is involved in the regulation of grain length and width in rice. It also functions as dominant regulator for grain shape. The marker RM3212 located on chromosome 2 was associated with medium-grain phenotype (Zhang et al.,2013). This marker expressed 181bp of allele size in rice and peanut.
GS3 (Grain Size) linked markers are RGS1, SF28, RGS2 and SR17. GS3 was not detected in African cultivars of rice (O.glaberrima and O. barthii) due to domestication process whereas the wild relative of rice O. meridionalis has unique alleles with respect to GS3 and shares the genome of AA with O.sativa which represent good candidate gene for genetic improvement of cultivated lines. Allelic variations at three loci including SF28, RGS1, and RGS2 in GS3 were highly associated with grain length, and explained a large portion of the variations in the mini-core collection of Chinese rice germplasm. SR17 has marginal effect to grain length (Wang et al.,2010).RGS1 is well predictive of medium to short grain length in rice. In the present study it amplified 180bp and 200bp allele sizes. SR17 amplified 1400bp of allele size, only in rice (Supplementary Fig. 4). These two markers regulate grain size as well as grain length in rice.
GS5 (Grain Size) encodes putative serine carboxypeptidase and regulates grain width positively. Overexpression of GS5 results in increased grain width (Li et al., 2011).Four markers RM574, RM593, C62, GS5-INDEL1 were used for genotyping analysis. Of these, C62 marker didn’t show any amplification. RM593 marker amplified with a size of 279 bp only in rice(Supplementary Fig. 4).GS5-INDEL1 amplified an allele with a size of 67bp in all the genotypes of rice and peanut which suggests that transferability of marker can be possible from rice to peanut. This 67bp allele size indicates wide grain(ST6) size as reported in Kim et al., 2016(Fig. 3). Hence, identification of functional variation in this gene might help in tagging of seed size in groundnut.
RM574 which is closely tagged to GS5 locus expressed 240bp of allele size in all genotypes of both rice and peanut (Fig. 3). This allele is usually associated with low grain width/size and can be used for rejecting at seedling stage in marker assisted breeding for high grain width character (Bidanchiet al., 2018) in rice. Characterizing of this gene in groundnut would reveal kernel size governing allelic variants.
GW2 (Grain Width and Weight) encodes a Ring type E3 ubiquitin ligase which functions in protein degradation pathway. This enzyme negatively regulates cell division and GW2 mutant allele promotes spikelet hull cell division which results in increase of grain width and grain weight (Song et al., 2007). GW2SNP2 marker expressed 51bp of allele size in both rice and peanut genotypes (Fig. 3) as reported same allele size in Zhang et al., 2015, by showing Kasalath with 51bp allele size whereas TD70 showed 30 and 21bp fragment after digestion with ApoI. The STS marker GW004 was used for amplification of GW2 gene which enhances grain width and yield. This marker reported the alleles of 750bp and 1050bp (Ngangkhamet al., 2018) in rice. In our study this marker expressed 750bp only in rice, which denotes lower grain width but not in groundnut (Supplementary Fig. 4).
GW5 (Grain Width and Weight) is associated with grain width or seed width. RM3328 which is linked to GW5at 2.3cM was selected for analysis of GW5 gene region. This expressed 119bp product size in rice (as same in Wang et al., 2008) and 95bp allele size in cultivated peanut genotypes whereas wild groundnut didn’t show any allele (Supplementary Fig. 3). The gene couldn’t reveal similar allele pattern, as there might be presence of indels in the region. The sequence analysis of the allele can show the possible reason behind allele change or entirely off-target by the marker.
Another marker RMw513, which is closely linked (0.37cM) to GW5 was selected for molecular analysis. This marker expressed 600bp allele size in both rice and cultivated peanut genotypes along with additional lower size alleles. The wild peanut showed 700bp of allele size (Fig. 3). RMw513 marker is associated with multiple traits such as grain width (GW), length- width ratio (LWR) and degree of endosperm chalkiness (DEC). RMw513 is used in MAS for developing slender grain and low chalkiness (Zhao et al.,2015) in rice. Analysis of the GW5 ortholog in peanut might help to unravel the seed size variation.
SW5 (Seed Width) N1212 marker linked to SW5 is associated with increased grain width. In the research conducted by Shomuraet al. (2008) between Nipponbare and Kasalath, Nipponbareharbored a 1212bp deletion and this deletion is Functional Nucleotide Polymorphism (FNP) for qSW5. This marker expressed 759bp product size in case of Nipponbare compared to 1971bp in Kasalath (Zhang et al., 2015). But in our study this marker expressed 65 bp product as major allele in all genotypes of rice and peanut (Fig. 3).
Single major QTL ( qsgw7) was identified on short arm of chromosome 7which deals with 1000-grain weight. Grain weight is directly associated with increased yield. The markers RM22015 and RM21997 which are closely linked to this gene were determined by Bian et al., 2013. Amplification with RM22015 marker amplified 176bp of allele size only in rice genotype in the study but not in groundnut (Supplementary Fig. 4)
GLW7 (Grain Length and Width) encodes plant specific transcription factor OsSPL13, which helps in regulating cell size in grain hull that inturn enhances grain length and yield. This belongs to SQUAMOSA PROMOTER BINDING PROTEIN (SBP) family and plays an important role in plant growth and development. OsSPL13 has a critical factor in the divergence of tropical japonica and temperate japonica, providing the opportunity to improve grain size and grain yield for a majority of temperate japonica varieties by introducing the large-grain OsSPL13LGH allele when breeding new elite rice varieties (Si et al., 2016). This marker expressed 140bp size in both rice and peanut. However, some genotypes of cultivated peanut viz., TPT-4, Kalahasti, Abhaya, TCGS894,TCGS1157 showed 160bp of allele size(Supplementary Fig. 3).This might give an assumption that variations occurred at the locus among groundnut genotypes. In-depth study of the gene will facilitate thorough understanding of its function in peanut.
RM505 linked to qgrl7 responsible for grain length was selected for genotype analysis. This marker amplified 220bp in Sonasal (short grain), 170bp in Chiguhong (grain plumpiness) and 180bp in PB1121(extra-long slender grain)(Deepti et al.,2012;Liu et al.,2017). In our study this marker expressed 500 and 180bp in rice and 490bp in cultivated peanut genotypes whereas no amplification is seen in wild peanut and TPT 1 (Fig. 3). Apart from major allele, non-specific amplification observed in peanut at low intensity. However, sequencing of the major allele can establish the ortholog nature of the gene in groundnut.
The other marker RM21945 present on chromosome 7 responsible for grain length and also quality parameter like Gel Consistency was selected and further analysed. This marker expressed 292bp of allele size for the trait of Gel Consistency. This marker is also associated with grain weight (GW), length and width ratio (LWR) (Zhao et al.,2015; Verma et al.,2015). In our study also, this marker amplified 292bp in all the genotypes of rice and peanut but with low intensity in peanut, as the reasons explained earlier (Supplementary Fig. 3). These results can suggest us that transferability is possible from rice to peanut once analysed with additional set of markers.
Seed Filling
Shelling percentage is an important trait to be considered in groundnut. The rice GRAIN INCOMPLETE FILLING 1 (GIF1) gene was considered to identify the ortholog in groundnut. GIF1 of rice encodes cell wall invertase and is responsible for grain filling and grain weight in rice. Mutation in GIF1 results in slower grain-filling which inturn reduces the glucose, fructose and sucrose levels in gif1 mutants (Wang et al., 2008). This marker expressed96bp of allele size in all the genotypes of both rice and peanut (Greeshma with low intensity) (Fig. 3), which suggests that transferability of gene that might govern seed filling/size can be possible.The other marker which is closely linked to GIF1 was RM16942. This marker expressed 181bp of product size only in rice but not in peanut.
Flowering Time
Groundnut is majorly a rainfed crop in India. Hence, early flowering and short breeding cycle is desirable trait among farmers. Heading date or Flowering time determines the beginning of the reproductive cycle and is greatly affected by environmental conditions (e.g. day length and temperature. HEADING DATE 3a (Hd3a) and RICE FLOWERING LOCUS T (RFT1) are homologs of FLOWERING LOCUS T (FT) in Arabidopsis (Takahashi and Shimamoto, 2011) and act as florigen genes to accelerate flowering (Ye et al., 2018). Hd3a promotes heading under short day conditions, whereas RFT1 is a major floral activator under long day conditions. Hd1, a homolog of CONSTANS in Arabidopsis, promotes flowering under short day conditions and reduces flowering under long day conditions by regulating the expression of Hd3a (Yano et al., 2000). Similarly rice Hd1 to wheat- TaHd1 (Nemotoet al., 2003) was identified.These results will boost the assumption of identification of peanut orthologs to rice. In our study, different markers related to heading date viz., Hd1, Hd1AGC,Hd3a and DTH8- INDEL were used.
Hd1 amplified 100 bp of allele size, only in rice. But these were not similar to reported size. The markers,Hd1AGC and Hd3a amplified 140bp and 90 bp respectively, in all the genotypes of rice and peanut with less intensity. Same size of allele can lead to the assumption of the presence of gene similar to rice. Sequencing of the alleles will confirm the assumption. Further, designing and use of additional markers targeting the gene can overcome the problem(Supplementary Fig. 3). Molecular characterization of these kinds of genes can help in designing the varieties with preferred duration.
Seed Micronutrient Content
Fe and Zn are important micronutrients towards human health, thus needs to be focused in research of food crops. For Fe and Zn content, primers using primer 3 software were designed for 3 reported genes viz., YSL2, YSL13 and YSL15 which belongs to Yellow-Stripe Like gene family. YSL2 gene reported for preferential expression in the leaf tissues which suggests that this YSL2 functions as transporter which is responsible for the phloem transport of iron. The other gene YSL15proved for its significant expression in root and rhizome type of tissues indicating its role in the uptake/absorption of iron from the source (Menna et al., 2011). Out of the five indel markers used, only one marker (vf0226164188) tagged to YSL2gene amplified alleles (137bp) in both rice and peanut (Fig. 3) and (Supplementary Fig. 4).
Assessment Of Cross Transferability Across Genotypes
From the results, overall transferability of markers under study and their possible utilization in peanut was assessed and are presented in Fig. 4 and Fig. 5. It is very interesting to note that amplification of 76% (31 out of 41 amplified markers) of rice gene tagged markers in groundnut was observed in initial standardization. This can be implied to highly conserved nature of functionally characterized genes between rice and peanut.
The extant of amplification of rice gene tagged markers among the peanut genotypes was assessed at individual genotype level from the current study, and allele code was assigned for each genotype (Table 4). The common allele sharing among the groundnut genotypes with rice was ranged from 79.17% (TCGS1157-Nithya Haritha, Greeshma, Prasuna, Kalahasti, Narayani and wild genotype A. villosa) to 91.67% (TCGS 1073 -Dheeraj) (Fig. 4). This further confirms the highest possibility of use of the rice markers/genes in groundnut.
Table 5
Total number of rice yield and seed quality gene orthologs found across Arachis hypogaea genome and their chromosome distribution
| Rice gene orthologs of A. hypogaea |
Chr | GW2 | GW5 | GW8 | GS2 | Sd1 | HD3A | Gn1a | OsSPL14 | Gene number per chromosome |
Chr 1 | 2 | 2 | 0 | 0 | 0 | 0 | 5 | 0 | 9 |
Chr 2 | 0 | 0 | 0 | 0 | 2 | 5 | 0 | 0 | 7 |
Chr 3 | 0 | 4 | 0 | 0 | 2 | 1 | 2 | 0 | 9 |
Chr 4 | 2 | 1 | 0 | 0 | 1 | 3 | 1 | 0 | 8 |
Chr 5 | 1 | 1 | 0 | 0 | 2 | 2 | 0 | 0 | 6 |
Chr 6 | 2 | 4 | 0 | 1 | 0 | 3 | 2 | 0 | 12 |
Chr 7 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Chr 8 | 1 | 0 | 0 | 0 | 1 | 2 | 2 | 0 | 6 |
Chr 9 | 1 | 0 | 0 | 0 | 2 | 0 | 1 | 0 | 4 |
Chr 10 | 2 | 1 | 0 | 0 | 1 | 2 | 2 | 1 | 9 |
Chr 11 | 2 | 3 | 0 | 0 | 0 | 0 | 6 | 0 | 11 |
Chr 12 | 1 | 2 | 0 | 0 | 1 | 3 | 0 | 0 | 7 |
Chr 13 | 1 | 2 | 1 | 0 | 3 | 1 | 2 | 0 | 10 |
Chr 14 | 1 | 0 | 0 | 0 | 1 | 3 | 0 | 0 | 5 |
Chr 15 | 0 | 1 | 0 | 0 | 2 | 2 | 0 | 0 | 5 |
Chr 16 | 1 | 6 | 0 | 1 | 2 | 3 | 2 | 1 | 16 |
Chr 17 | 0 | 0 | 0 | 0 | 1 | 1 | 2 | 0 | 4 |
Chr 18 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 1 |
Chr 19 | 1 | 0 | 0 | 0 | 2 | 1 | 0 | 0 | 4 |
Chr 20 | 2 | 1 | 0 | 0 | 0 | 2 | 1 | 1 | 7 |
Total | 20 | 28 | 1 | 2 | 23 | 35 | 28 | 3 | 140 |
Further the transferable efficiency of individual marker revealed that a total of 17 markers pertaining to 14 genes (Fig. 5) showed amplification among all groundnut genotypes (100%). However, two markers Dep1 INDEL 1 and Hd1 showed 6% amplification only. Of 17 markers, few of which (SCM2INDEL, Hd3A, Hd1AGC) showed the amplification at low intensity yet retained the allele size of rice. Hence, designing/use of markers from rest of the gene sequence would resolve the amplification problem.
Insilico Analysis
Insilico analysis of groundnut genome with the help of Peanutbase(https://peanutbase.org/search/gene) and NCBI (https://blast.ncbi.nlm.nih.gov/Blast.cgi) revealed large number of rice yield gene orthologs. From the Peanutbase, the analysis has identified 140 rice gene orthologs of Arachishypogaea for different traits (Fig. 6). Of which, eight grain size related genes viz., HD3A(35 genes), GW5(28 genes), Gn1a(28 genes), sd1(23 genes), GW2(20 genes), OsSPL14(03 genes), GS2(02 genes) and GW8(01 gene) genes were identified, with greater number (79)of peanut orthologs i.e. 56.43%.Remaining genes are found with plant architecture governing genes.The gene distribution on different peanut chromosomes is shown in the Fig. 6. The total of 140 genes fell on all chromosomes except Chr 7. Chromosome 16 contains highest number (16) of orthologous genes followed by Chr 6 with 12 genes. Only one orthologous gene was identified for GW8 on chromosome 18. Physical location of genes was given in Supplementary Table 3.
By Insilico analysis, we identified 20 Ubiquitin ligase genes (GW2 orthologs) located on 14 different chromosomes (Chr 1,4,5,6,8,9,10,11,12,13,14,16,19 and 20) in peanut pertaining to Grain weight/seed weight (Supplementary Table 3). These functionalized genes are reported to increase cell number and also regulate cell division. Characterizing these genes will help to regulate seed weight in peanut. Recently Wang et al. (2021) also proved similar kind of results with peanut seed transcriptome study.
Primer blast analysis of NCBI database with rice gene tagged primers under study, for expressed sequences/transcripts of groundnut genome also revealed the presence of huge number of functional rice yield gene orthologs for diverse traits(Fig. 7).
Studies have proved the transfer of knowledge of functionally characterized genes of Rice (poaceae) to other plant families. For instance, grain size (GS2) of rice to fruit size (OVATE) of Tomato (Gupta et al., 2006.), tillering of rice (MOC1) to Lateral suppressor (Ls) gene of tomato (Hussienet al., 2014).
The studies on utilization of homolog genes proved the conservation of coding sequences between rice and other cereals/millets. For instance, study on identification and utilization of rice grain width and weight gene (GW2) homologs in maize revealed the presence of two genes viz., ZmGW2 on CHR4 and ZmGW2 on CHR5 (Li et al., 2010). Sequence analyses of these genes showed highly conservedcoding regionwith an overall similarity of 94% with rice wherein the functional protein domains of both genes are completely conserved, with no non-synonymous polymorphisms identified, which suggests that both genes have conserved functions across genera.
Nemotoet al. (2003) also isolated three kinds of Hd1 orthologs from wheat TaHd1-1, TaHd1-2, TaHd1-3 derived from A,B and D genomes respectively. When they introduced TaHd1-1 into Hd1 deficient rice line, transgenic plants complemented the functions of Hd1 promoting heading under short day conditions and delayed under long day conditions.Further, the research on Hd1 of rice found that Hd1 is a homolog of CONSTANS (CO)gene ofArabidopsis and encodes a protein with a zinc finger domain. Sequence comparison of Hd1 with that of CO from Arabidopsis found 59% identity in the zinc finger domain and 79% identity in the C-terminal region.
Collinearity of cereal and legume genomes analysed with genomic sequences of molecular model crops also proved to have similarity of over 40% (Supplementary Table 4).Interestingly, Hussienet al., 2014 characterized Rice-nodulation signaling pathway genes NSP1 and NSP2and identified the orthologs in Legumes viz., Legume-NSP1 and Legume-NSP2.This study proved the transferability of known gene knowledge from rice to legumes.