DOI: https://doi.org/10.21203/rs.3.rs-1405748/v1
Background
Alfalfa (Medicago sativa L.) is the most cultivated forage legume around the world. Under a variety of growing conditions, forage yield in alfalfa is stymied by biotic and abiotic stresses including heat, salt, drought, and disease. Given the sessile nature of plants, they use strategies such as differential gene expression to respond to environmental cues. Transcription factors control the expression of genes that contribute to or enable tolerance and survival during periods of stress. Basic-leucine zipper (bZIP) transcription factors have been demonstrated to play a critical role in regulating plant growth and development as well as mediate the responses to abiotic stress in several species, including Arabidopsis thaliana, Oryza sativa, Lotus japonicus and Medicago truncatula. However, there is little information about bZIP transcription factors in cultivated alfalfa.
Result
In the present study, 237 bZIP genes were identified in alfalfa from publicly available sequencing data. Multiple sequence alignments showed the presence of intact bZIP motifs in the identified sequences. Based on previous phylogenetic analyses in Arabidopsis thaliana, alfalfa bZIPs were similarly divided and fell into 10 groups. The physico-chemical properties, motif analysis and phylogenetic study of the alfalfa bZIPs revealed high specificity within groups. The differential expression of alfalfa bZIPs in a suite of tissues indicates that bZIP genes are specifically expressed at different developmental stages in alfalfa. Similarly, expression analysis in response to ABA, cold, drought and salt stresses, indicates that a subset of bZIP genes are also differentially expressed and likely play a role in abiotic stress signaling and/or tolerance.
Conclusions
Taken together, this work provides a framework for the future study of bZIPs in alfalfa and presents candidate bZIPs involved in stress-response signaling.
Alfalfa (Medicago sativa L.) is a perennial and highly outcrossing forage legume crop grown predominantly for hay, silage, and pasture. It is the most widely cultivated forage legume in the United States with approximately 16 million hectares planted (1). The high nutritional value of alfalfa with about 15–22% crude protein and an abundance of vitamins and minerals makes it well suited for animal and livestock feed. Alfalfa also brings long-term ecological benefits to society by improving soil fertility through its symbiotic association with the soil bacterium Sinorhizobium meliloti for atmospheric nitrogen fixation, which augments the nitrogen content in the soil for future crops (2–4). The perennial nature of alfalfa along with its deep root system (up to 15 m) helps to prevent soil erosion. However, genetic improvement in terms of forage yield has been relatively stagnant in alfalfa (1).
In fact, the high out-crossing nature, genomic complexity, severe inbreeding depression upon selfing and self-incompatibility complicates alfalfa breeding. Although the multi-purpose use of alfalfa is increasing in demand, production is hindered by changing environmental conditions leading to abiotic stresses like heat, drought, and salinity. In the context of stagnant genetic improvement, cultivation of stress-resilient alfalfa germplasm will help to improve production in response to climate change. However, identification of stress-resilient germplasm requires identification of stress-responsive genes, which, in alfalfa, are very few due to incomplete genomic information and limited expression profile data.
The sessile nature of plants inevitably exposes them to adverse environmental conditions such as abiotic stress. Plants have developed diverse mechanisms to cope with these abiotic stresses. One mechanism is the synthesis of proteins, metabolites, and other compounds to aid in survival through abiotic stress, which are often controlled by transcription factors (TFs). Transcription factors play a critical role in responses to environmental stresses via binding to cis-regulatory elements in promoters to regulate downstream gene expression. In plants, approximately 7% of the genome codes for transcriptional regulators, which bind promoter elements of downstream genes through their conserved sequence specific DNA-binding domain (5). Among the 64 families (6) of transcription factors identified in the plant kingdom, the bZIP (basic leucine zipper) family is one of the largest and most diverse (6–8).
The basic leucine zipper (bZIP) family is distinguished by its highly conserved bZIP domain composed of 60–80 amino acids (9). Structurally, the bZIP domain is divided into two functionally distinct regions: a basic region and a leucine zipper motif (9). The basic region is composed of an invariant motif (N-x7-R/K-x9) of 18 amino acids residues that facilitates sequence-specific DNA binding, while the leucine zipper contains several heptad repeats of leucine or other bulky hydrophobic amino acids such as isoleucine, valine, phenylalanine, or methionine, for dimerization specificity (7, 10). Molecular studies of bZIP genes in Arabidopsis thaliana show that they are involved in the regulation of diverse biological processes including pathogen defense, light and stress signaling, seed maturation and flower development (10). Additional information on the bZIP transcription factor family has provided evidence of their role in response to biotic and abiotic stresses in a diversity of plant species (10, 11).
The availability of whole genome sequences for plants allows the identification or prediction of bZIP TF family members at the genome-wide level. The number of bZIP TFs identified in different plant and crop species varies from 78 (AtbZIPs) in Arabidopsis thaliana (8), 89 (OsbZIPs) in Oryza sativa subs. japonica (7), 125 (ZmbZIPs) in Zea mays (11), 131 (GmbZIPs) in Glycine max (12), 92 (SbbZIPs) in Sorghum bicolor (13), 55 (VvbZIPs) in Vitis vinifera (14), 64 (CsbZIPs) in Cucumis sativus (15) and 247 (BnbZIPs) in Brassica napus (16). The bZIP transcription factors play crucial roles in developmental processes and environmental tolerance in response to multiple stresses. They are involved in the regulation of seed development (17, 18), cell elongation (19, 20), vascular development (20), flower development (21–24), somatic embryogenesis (25), as well as in nitrogen/carbon and energy metabolism (26–28).
In addition to functions in plant growth and development, bZIPs also play an important role in responses to abiotic and biotic stresses. Several bZIPs from A. thaliana (AtbZIP17, AtbZIP24, AtbZIP12), rice (OsbZIP12, OsbZIP72, OsABF1) and soybean (GmbZIP44, GmbZIP62, GmbZIP78) were found to positively regulate salt stress adaptation in plants either directly or indirectly (12, 29–34). Several bZIPs from rice (OsbZIP52/RISBZ5, OsbZIP16, OsbZIP23, OsbZIP45, AREB1, AREB2, ABF3) were also found to be involved in drought tolerance (35–38). OsbZIP52/RISBZ5 negatively regulates cold stress responses (36) while OsbZIP72 was a positive regulator of ABA responses (33). Similarly, overexpression of GmbZIP44, GmbZIP62 and GmbZIP78 reduced ABA sensitivity (12). Interestingly, group D or so-called TGA bZIPs plant a role in systemic acquired resistance (SAR) and pathogen resistance (39, 40). However, there is little published information about the bZIP transcription factor family in cultivated alfalfa and its role in stress resistance.
With the availability of a chromosome-level genome assembly in alfalfa (41) we conducted a genome-wide search to identify and characterize the alfalfa bZIP transcription factors. Since bZIP transcription factors were identified to play significant roles in the regulation of abiotic stress tolerance (10, 11), we speculated various bZIP transcription factors would be differentially expressed throughout distinct developmental stages and abiotic stresses in alfalfa as well. The present study identifies several bZIPs from a proteomic database in tetraploid alfalfa (Medicago sativa). We also analyzed differential gene expression from transcriptome sequences during ABA, drought, salt, and cold stress conditions. This study will facilitate functional analysis of the bZIP transcription factor family in alfalfa. The identification of functions of alfalfa bZIP transcription factors during abiotic stress conditions will further help breeding efforts for improved stress tolerance.
For comprehensive identification and analysis of the bZIP transcription factor (TF) gene family in alfalfa, the sequences of bZIP transcription factors from model and known species were downloaded from the Plant Transcription factor database (http://planttfdb.cbi.pku.edu.cn/), which included 127 sequences from Arabidopsis thaliana, 93 from Lotus japonicus, 124 from Medicago truncatula and 140 from Oryza sativa. The number of bZIPs used were more than that is mentioned in Table 1 as it included spliced variants as well. A local protein database was created using Basic Local Alignment Search Tool (54) with protein sequences from chromosome level assembly of alfalfa (41). A BLASTp search was conducted in the local database created using the protein sequences from alfalfa, taking the bZIP sequences from model organisms as a query with an E-value cut-off of 1E-05 (0.00001). The bZIP sequences obtained from the search were further confirmed based on the presence of the bZIP domain (N-x(7)-R/K-x(9)-L-x(6)-L-x(6)-L) using the Pfam web program (https://pfam.xfam.org/) with an E-value of 1.0. Further, the bZIP domain was used to search against the database of the identified bZIP sequences using the Prosite program of the ExPASy bioinformatics resource (http://protsite.expasy.org). The identified sequences with intact bZIP domains were predicted to be bonafide bZIP sequences.
To analyze the sequence features of bZIP transcription factors, multiple sequence alignment of 237 bZIP proteins were performed using multiple sequence comparison by log-expectation (MUSCLE) (55) command using default parameters. The output of the multiple sequence alignment was visualized using Unipro UGENE v.33. (56) For evolutionary analysis, 549 sequences were used which included sequences from Medicago sativa (237), Arabidopsis thaliana (78), Lotus japonicus (70), Medicago truncatula (75) and Oryza sativa (89). Multiple sequence alignment was carried out by CLUSTALW with default parameters. Subsequently, the phylogenetic tree was constructed by the Neighbor Joining method using 1000 bootstraps replicates. Phylogenetic analyses were conducted using MEGA version X (57).
Other physical properties of the identified sequences like the molecular weight and theoretical isoelectric point (pI) were determined using Compute pI/Mw tools (http://web.expasy.org/compute_pi/) of ExPASy bioinformatics resource. The MEME (44) program was used to identify the conserved motifs within the full-length Alfalfa. The parameters used were maximum number of motifs to be 25, distribution of motifs = any number of repetitions, optimum motif width = 6 to 50 residues.
For predicting the MsbZIP protein function (gene ontology) GO annotation was performed using the web-accessible Blast2GO v4.1 annotation system (https://www.blast2go.com/) (58). Briefly, the MsbZIP protein sequences were used to search for similar sequences against the NCBI non-redundant (Nr) database using the Blast tool in the Blast2GO software, with an E-value of 10 − 3 (1e-03). Next, mapping and annotation were performed on Blast2GO using default parameters. Finally, functional classification was also performed by Blast2GO.
The raw RNA sequence data was downloaded from the National Center for Biotechnology Information (NCBI) Sequence Read Archive (SRA), SRP055547 (45). The data was generated from six tissues at different growth stages of Alfalfa namely, root, nodule, elonged stem, pre-elonged stem, leaf, and flower. The tissue sample for RNA-Seq was collected at the respective stage of alfalfa plants. Fastqc version 0.11.7 was used for quality check of the raw sequences. The reads passing the minimum Phred quality score of 30 were selected. The RNA-Seq analysis was carried out following the method described by (59), in which the filtered reads were aligned with the reference genome using HISAT2 version 2.1.0 (60) and sorted by Samtools ver 1.9. Transcript assembly and quantification was carried out using Stringtie version 2.1.1 (61). A python script was used to extract read count information directly from the files generated from Stringtie and edgeR package (62) in R was used for differential gene expression analysis. TBtools version 1.0692 (63) was used to generate heatmaps for the differentially expressed genes.
The raw RNA sequence data from previous studies were downloaded from the National Center for Biotechnological Information (NCBI) Sequence Read Archive (SRA). The transcriptome data consist of cold treatment (SRR7091780-SRR7091794, (64, 65), and ABA, drought, and salt treatments (SRR7160313-SRR7160357, (64, 66). All these samples were collected from 12 days old alfalfa seedlings for RNA-Seq. Fastqc version 0.11.7 was used for quality check of the raw sequences. The reads passing the minimum Phred quality score of 40 were selected. The RNA-Seq analysis was carried out following the method described by (59), in which the filtered reads were aligned with the reference genome using HISAT2 ver2.1.0 and sorted by Samtools ver1.9. Transcript assembly and quantification was carried out using Stringtie version 2.1.1. A python script was used to extract read count information directly from the files generated from Stringtie and edgeR package in R was used for differential gene expression analysis. TBtools version 1.0692 was used to generate heatmaps for the differentially expressed genes.
For this analysis, the bZIP genes with changed expression during abiotic stress were visualized using Integrated Genome Browser 9.1.4 (67) to locate the promoter sequences. Samtools (ver. 1.9) was used to extract the 2000 base pair sequence from the promoter of these changed bZIP genes to investigate the potential cis-regulatory elements by querying them through the PlantCARE database (http://bioinformatics.psb.ugent.be/webtools/plantcare/html/). In total six cis-regulatory elements responsive to stress were analyzed. These elements included abscisic acid responsive (ABRE), methyl jasmonate responsive (CGTCA-motif), light inducible G-box motif, low-temperature responsive (LTR), drought responsive (MBS binding site) and defense and stress responsive (TC-rich repeats).
We identified 237 bZIP sequences with the intact bZIP domain in alfalfa (Medicago sativa). These sequences were named MsbZIP1 to MsbZIP237 based on the order identified in the protein sequence database (41). We compared the genome size and number of bZIPs in different models and crop species (Table 1). The comparison shows that alfalfa has the highest number of bZIP sequences. Since the diploid model legume Medicago truncatula with genome size of 390 Mega Base (Mb) has 75 bZIP sequences, tetraploid alfalfa is expected to have double the number of bZIP sequences. Not surprisingly, the number of bZIP TFs identified in alfalfa was 237, which likely represents the complete number of bZIP for tetraploid alfalfa.
| Species | Chromosome | Genome Size | Number of bZIPs |
|---|---|---|---|
| Arabidopsis thaliana (8,10) | 2n = 2x = 10 | 135 Mb | 78 |
| Brassica napus (16) | 2n = 2x1 + 2x2 = 38 | 1.16 Gb | 247 |
| Lotus japonicus (6) | 2n = 2x = 12 | 470 Mb | 70 |
| Medicago truncatula (42) | 2n = 2x = 16 | 390 Mb | 75 |
| Oryza sativa (7) | 2n = 2x = 20 | 430 Mb | 89 |
| Medicago sativa (Current Study) | 2n = 4x = 32 | 3,150 Mb | 237 |
To identify common conserved domains amongst the sequences, we carried out multiple sequence alignment. The alignment of 237 bZIP protein sequences showed the presence of intact and highly conserved bZIP domains (N-x(7)-R/K-x(9)-L-x(6)-L-x(6)-L) (Fig. 1, Supplementary Fig. 1). The domain is divided into the basic region with ~ 18 amino acids residues containing nuclear localization signal followed by an intact N-x(7)-R/K motif while the leucine zipper region contains heptad repeats of leucines or other bulky hydrophobic amino acids with nine amino acids towards the C-terminus (10). The presence of the intact bZIP domain further validates the identified sequences as bZIP proteins. The identified 237 bZIP proteins were divided into 10 groups (A, C, D, E, F, G, H, I, M, and S) based on the topology of the tree developed in Arabidopsis thaliana (8, 10) and were used to generate a phylogenetic tree along with protein sequences from Arabidopsis thaliana, Lotus japonicus, Medicago truncatula and Oryza sativa (Fig. 2). Alfalfa bZIP proteins fell into 10 different groups and numbers ranged from four (H) to forty-three (A); however, no members were identified for groups B, J and K.
Identification of conserved protein motifs helps to elucidate protein functions and bZIPs usually possess additional conserved motifs that could provide sites for activation (43). Using the “MEME” (Multiple Em for Motif Elicitation) program (44), 25 conserved motifs were identified in the 237 bZIPs (Supplementary Table 2). Among the identified motifs, the basic region of the bZIP, containing an invariant motif (N-x7-R/K-x9) with 18 amino acid residues was found (Fig. 3A), while the leucine zipper region that contains the heptad repeat of leucine or other bulky hydrophobic amino acids was also identified (Fig. 3B). The basic region facilitates sequence specific DNA binding whereas the leucine zipper region is important for dimerization specificity. However, the function of the 23 motifs that were also identified in the bZIP sequences are unknown and require further study.
Among the 237 MsbZIP, 21 GO (Gene Ontology) categories were assigned to 203 of the MsbZIPs identified (Fig. 4). The major molecular functions of these bZIPs were DNA-binding transcription factor activity, which is consistent with their demonstrated role as transcription factors in other species. In the biological process category, most of bZIPs were assigned to the regulation of transcription category and almost all these proteins were predicted to localize to the nucleus in the cellular component category. Transcription factors provide binding sites through which they can regulate gene expression. They may act as either positive or negative regulators of downstream genes depending upon the environmental condition. The current functional classification (GO terms) of these bZIP proteins further supports their regulatory nature.
After analysis of publicly available RNA-Seq data (45), we found differential expression of 177 bZIP genes. These genes were selected for having expression values in at least one of the tissues: stem, flowers, leaves, root nodules, roots, and pre-elongated stems (PES). They were then displayed in a heatmap to visualize the expression profile in different tissues and organs (Fig. 5). Differential gene expression was observed for different developmental stages. Most of the genes were highly expressed in nodules and roots. Apart from nodules and roots, genes that were upregulated in one developmental stage were downregulated in other developmental stages which can be observed in the heatmap. Even within a group, the genes were differentially expressed across all developmental stages suggesting different bZIP genes are required for growth and development at different stages.
Analysis from the publicly available RNA-seq datasets showed differential expression of 146 genes during ABA, drought, and salt stress as well as 152 bZIP proteins during cold stress at 0, 2, 6, 24, and 48h, respectively. The expression pattern of MsbZIP genes during different abiotic stress conditions of cold, ABA, drought and salt showed differential expression. Across different time points of abiotic stress, the expression was different for different genes and even within a group the genes were expressed differently for different abiotic stress. Among 4 different time points of cold treatment (2h, 6h, 24h and 48 h), different genes were upregulated at different time points (Supplementary Fig. 2). Even within a group, at different time points, different genes were upregulated and downregulated at different intervals of cold treatment. Like the cold treatment, abiotic stress of ABA, drought and salt treatment also showed multiple genes upregulated at different time points of stress treatment (Fig. 6). However, no genes were actively expressed during different time points of the same treatment condition among ABA, drought, and salt, which indicates different transcription factors are active during different abiotic stress as well as different time points of stress.
The expression pattern of stress responsive-genes are often controlled by cis-regulatory elements. These elements are typically located 5’ upstream of the gene coding sequences. These elements provide a binding site for the transcription factors to switch on or off the gene based on the environmental condition. In this study, we analyzed 135 stress-responsive bZIP promoters, we identified 875 cis-regulatory elements distributed along these 135 bZIP promoter. The detailed distribution of these cis-elements along the bZIP promoters was performed (Supplementary Fig. 3). We focused on cis-elements implicated in abiotic stress responses and found an abundance of the following cis-regulatory elements: abscisic acid responsive element (ABRE), methyl jasmonate responsive motif (CGTCA-motif), light inducible G-box motif, low-temperature responsive (LTR), drought responsive (MBS binding site) and defense and stress responsive (TC-rich repeats).Among the 875 cis-elements, light inducing G-box motif was the highest with 274 followed by abscisic stress responsive element (ABRE) with 234 while low temperature responsive (LTR) with 50 was the lowest.
In the present study, we identified 237 bZIP sequences from tetraploid alfalfa that contained both a highly conserved basic region and the heptad repeat leucine zipper region, suggesting they are functional bZIPs. As predicted, the number of bZIP in tetraploid alfalfa (237) is more than double to that of diploid model legume Medicago truncatula (75). Not surprisingly, the number of bZIP genes varied amongst plant species with Arabidopsis thaliana (78), Lotus japonicus (70), Medicago truncatula (75) and Oryza sativa (89) (6, 10, 42, 46, 47). Similarly, the allotetraploid B. napus genome contained 247 bZIP genes, which is roughly double that of the number found in the related diploid A. thaliana.
Based on phylogenetic analysis and previous analyses from A. thaliana, Medicago truncatula, Lotus japonicus and Oryza sativa, we classified the alfalfa bZIP genes into 10 groups (A, C, D, E, F, G, H, I, M, and S). The most recent classification of bZIPs from A. thaliana (8) sorted AtbZIPs into 13 groups. Notably, groups B, J and K are missing in our analysis of alfalfa. In A.thaliana there are three members of group B (bZIP17, bZIP28, and bZIP49) and one group K member (bZIP60), which are implicated in endoplasmic reticulum stress responses (48), but both these groups are missing in alfalfa which begs the question of which groups perform this function in alfalfa. Group J in A. thaliana is made up of a single copy gene, bZIP62, which is related to Group G bZIP GBF1– a negative regulator of blue-light responsive hypocotyl growth that acts antagonistically to HY5 and HYH, two group H bZIPs important in photomorphogenic growth (49). Another remarkable difference between groups is the group M bZIP72, which is single copy in A. thaliana but contains 13 members in alfalfa. It will be interesting to determine the role M group bZIPs play in alfalfa and it is intriguing to postulate why this group has increased in number.
It is well established that bZIP transcription factors have a myriad of roles in plant development such as seed maturation and germination (18), floral induction and development (21, 24). Not surprisingly, tissue-specific expression of 177 bZIP genes in nodules, flowers, roots, leaves, and stems was found in alfalfa as well (Fig. 5). Interestingly, group E members were most specifically expressed in stems, roots, and flowers, whereas several group F members were expressed in pre-elongated stems. In A. thaliana the group E member bZIP34 has been linked to pollen germination and pollen tube growth (23). In contrast, group F members regulate zinc (Zn) transporters and salt stress responses (34, 50). Group C and S bZIPs are known to heterodimerize in the so-called C/S1 bZIP network involved in nutrient and energy metabolism (28, 51). Likewise, group C and S bZIPs are co-expressed in some tissues such as roots and nodules in alfalfa.
In addition to regulating development, bZIPs play a wide array of roles in biotic and abiotic stress responses (10, 11) in different crop species. Zou et al., (2008) (52) identified the OsABI5 bZIP TF that was involved in rice fertility and stress tolerance. Nijhawan et al., (2008) (7) related bZIP genes in rice to drought tolerance through genomic survey and gene expression analysis. Similarly, a root-specific bZIP transcription factor was isolated in tepary beans and found to be responsive to water-stress conditions (53). Liao et al., (2008) (12) isolated three bZIP genes (GmbZIP44, GmbZIP62, GmbZIP78) and found a negative regulator of ABA and tolerance to salt and freezing stress by over-expression in A. thaliana. As several studies have shown the role of bZIP transcription factors in the response to plant stress, Liu et al., (2012) (36) further added to it by cloning a bZIP gene and measuring physiological changes mediated by it in alfalfa under different stress conditions. Additionally, they over-expressed cloned alfalfa bZIP genes in tobacco plants which resulted in transgenic tobacco plants conveying salt and drought tolerance. These results indicate that over-expression of certain bZIP genes increases tolerance of plants to different abiotic stresses. In the present study, MsbZIP genes were found to be differentially expressed in response to cold, ABA, drought and salt indicating the involvement of distinct bZIPs in response to abiotic stresses. Notably, group A MsbZIP88 was strongly upregulated in response to 24h salt stress and in Arabidopsis group A members are involved in ABA signaling and abiotic stress responses. Similarly, another group A member MsbZIP80 showed upregulation 3h of ABA treatment as well as 3h drought exposure. Our results are in line with previously published work on bZIPs in abiotic stress responses and provide candidates for functional analyses in alfalfa.
Here we report the first comprehensive analysis of the bZIP transcription factor family in alfalfa (Medicago sativa). We identified 237 bZIP genes and named them MsbZIP1 to MsbZIP237. Phylogenetic analysis of these bZIP genes using Arabidopsis thaliana as reference divided the sequences into 10 groups, with B, J, and K missing in alfalfa. The physico-chemical analysis and motif analysis showed high specificity within each group. The expression profile of bZIPs from suggest bZIPs are expressed in a tissue-specific manner. Finally, the expression profiles of bZIP genes during different abiotic stress conditions (cold, ABA, drought, and salt) showed specific response of a few bZIP at specific timepoints during the stress response making them good candidates for stress-responsive transcription factors. Taken together, this work provides a framework for the future study of bZIPs in alfalfa and presents candidate bZIPs involved in stress-response signaling.
ABA: Abscisic acid
BLAST: Basic local alignment search tool
bZIP: Basic-leucine zipper
DNA: Deoxyribonucleic acid
GO: Gene ontology
Mb: Mega base
MEGA: Molecular evolutionary genetics analysis
MEME: Multiple Em for Motif Elicitation
MUSCLE: Multiple Sequence Comparison by Log-Expectation
NASS: National Agricultural Statistics Service
NCBI: National center for biotechnology information
PES: Pre-elongated stem
RNA-Seq: Ribonucleic acid sequencing
SAR: Systemic acquired resistance
SRA: Sequence read archive
TFs: Transcription Factors
TGA: TGACG-Binding
USDA: United States Department of Agriculture
Zn: Zinc
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Availability of data and materials
The datasets generated and analyzed during the current study are available in the,
Plant Transcription Factor database (http://planttfdb.gao-lab.org/family.php?fam=bZIP),
Zeng, Yan (2020): genome fasta sequence and annotation files. figshare. Dataset., https://doi.org/10.6084/m9.figshare.12327602.v3
Raw reads for RNA-seq are available with Sequence Read Archive SRP055547, SRR7091780 to SRR7091794, and SRR7160313 to SRR7160357.
Competing interest
Not applicable.
Funding
This project was funded by USDA NIFA (Hatch project 1014919, 2018-70005-28792, 2019-67013-29171, and 2020-67021-32460), and Washington Grain Commission (Endowment and Awards #s 126593 and 134574)
Contributions
All Authors contributed equally to this work.
Acknowledgement
Not applicable