A comprehensive phylogenetic tree comprising 110 PvB3 protein sequences of common bean (Fig. 2).The phylogenetic tree was generated using the Maximun Likelihoodphy using WAG + G model in MEGA software (MEGAX) with the B3 sequences. Based on the phylogenetic tree, the predicted PvB3 family clustered into 4 subgroups, which is Ⅰ-ⅠⅤ. Subgroups Ⅰ and ⅠⅤ have the most PvB3 members, compared to subgroups Ⅱ and Ⅲ.
The motif and gene structure conserved PvB3 family members
We employed the MEME software to analyze the conservative motifs of 110 PvB3s in 4 subgroups in celery. Figure 3b shows the symbols of the motifs and the composition of every B3 family members in P.vulgaris.L. Each sub-group contains some differences in the motif, but the members within each sub-family have similar motif structures. For example, in the Ⅰ, Ⅱ, and Ⅲ subgroups all have motif 4, only members of subgroup 4 and a few members of subgroup 1 own motif 8, and the Ⅳ subgroup contains many different motifs, but every member of the Ⅳ subgroup owns these motifs.
The gene structure of exon and intron of the PvB3s were examined to reveal a certain difference in the gene structure among the 4 subfamilies, regardless of the length of their genetic structure, the number of introns and exons, including the number of CDS, but the structure of PvB3 in each subfamily is relatively consistent No matter the number of their CDS and introns, they are even similar to the position of B3 domain in their gene structure.
Cis-regulatory elements analysis of PvB3s
Cis-regulatory elements was used to be analyzed by PlantCARE software, according to the promoters of PvB3s according to the celery genome database, and the related hormone formation seed germination related elements are represented in Fig. 4b. Red boxes are hormone-related elements. These elements revealed that the PvB3s may respond to hormones in response to stress; The blue elements represent elements that respectively encounter low-temperature and drought, indicating that the PvB3s have a very important role in abiotic stress; yellow represents elements that are related to plant germination or sprout stage.
Collinearity analysis and tandem replication of PvB3s
The results of collinear analysis within common bean B3 family gene species and with legume crops and Arabidopsis thaliana are shown in Fig. 5. Only 14 pairs of bean B3 family genes were collinear and distributed in 11 LGs, of which 9 had the largest number of PvB3 with 4 members, indicating that PvB3s were not randomly and uniformly distributed on the linkage group (Fig. 5a). In legume species, there was collinearity between PvB3s and soybean 88 genes (G. max.L), adzuki bean 35 genes (V. angularis) and mung bean 50 genes (V. radiata.L) (Fig. 5b). However, only 23 genes in the B3 family of common beans are collinear with Arabidopsis thaliana,and only 5 genes in rice (O. sativa L.) (Fig. 5c). In the selection pressure analysis of PvB3s (Table S3), only 3 pairs of tandem replication genes in PvB3 had Ka/Ks < 1, while the Ka/Ks > 1 of 9 pairs of PvB3s.
Analysis of PvB3 members and the genes containing B3 domain in Arabidopsis
The same Pfam identified proteins and genes containing B3 conserved domains in Arabidopsis, and conducted evolutionary analysis of mixture species with PvB3 members, as well as motif and gene structure analysis (Fig. 6). After analysis, it was found that the B3 family genes of the two species are also divided into 4 subgroups, as PvB3s in. The genetic structure and motif of each subfamily are relatively similar, indicating that each subfamily is traveling The functions are relatively consistent.
Expression analysis of PvB3s in Different Tissues of Common bean in sprout stage
Successively, we examined the transcriptional patterns of PvB3s in many tissues using high-throughput sequencing information from Phytozome database, that included flower buds, flowers, leaves, root, trifoliates, nodules, stem, pod, seed, and other tissues (Fig. 7a), PvB3s are expressed in various tissues, and the expression differences are relatively large. To elucidate the functions of the PvB3 genes in P. vulgaris at sprout stage, we choose 6 PvB3 genes randomly, used qRT-PCR for three tissues (cotyledon, hypocotyl, radicle) in common bean R sprout stage to assess the expression of the PvB3 genes in sprout stage diverse tissues. As shown (Fig. 7b), among the 6 PvB3 genes randomly selected, The relative expression of some B3 family genes in the radicle is relatively high, and some PvB3s have relatively high expression in the hypocotyl.
Expression analysis of PvB3s in extreme materials under salt stress
From a laboratory basis, we tested two kinds of extreme common bean materials under water treatment and salt stress treatment (R is salt-tolerant variety, and N is salt-sensitive variety). The assembled unigene dataset was used as a reference for further analyses, and it can be found at the National Centre for Biotechnology Information under the accession number PRJNA558376 (http://www.ncbi.nlm.nih.gov/bioproject/). Through the determination of transcriptome, we found that there was a significant difference in PvB3s’ expression, but many PvB3s of the fourth subfamily are not expressed(Fig. 8a). 9 PvB3 genes were randomly selected for qRT-PCR analysis, and it was found that under W (water treated) and S (salt stress treated), the transcriptome results of PvB3 genes expression in extreme materials R and N were consistent (Fig. 8b). It is suggested that under salt stress, the differential expression of PvB3s in extreme materials may affect the salt tolerance of plants.
PvB3s expression analysis of IAA enrichment pathway in extreme materials under salt stress
The KEGG analysis of PvB3s showed that PvB3s were enriched into the pathway “Plant hormone signal transduction” (pvu04075) in common bean, and its Corrected P-Value was 1.81e-14(Fig. 9a). The result showed that PvB3s could adjust plant stomata in response to IAA. The IAA content of extreme materials was determined, and it was found that the IAA content of salt-resistant variety R itself was higher and increased sharply under salt stress, while the change of IAA content of salt-sensitive variety N was relatively small (Fig. 9b). The results of qRT-PCR analysis of radicles of two varieties showed that, compared with S treatment, some PvB3s the change of gene expression of R variety was larger than that of N variety, which indicated that the change of IAA content did affect the change of PvB3s under salt stress, which may further affect the salt tolerance of common bean at sprout stage (Fig. 9c).
The Relationship between IAA, salt stress and PvB3s
After IAA and salt treatment, the sensitive salt variety N has been alleviated a lot compared with S treatment, such as the number of lateral roots of bean sprouts increased significantly (Fig. 10a). Exogenous IAA could significantly increase the content of endogenous IAA in N varieties (Fig. 10b), and 8 PvB3s, were randomly selected and verified by qRT-PCR analysis (Fig. 10c). It was found that the variable of these genes increased or decreased significantly in N, indicating that PvB3s will respond to the changes of IAA to resist salt stress in plants.