Genome-wide identification of tomato B-RRs gene family and expression analysis in response to ABA and drought.

Abstract

B-type Response Regulators (B-RRs) play a crucial regulatory role in cytokinin signal transduction and are significant for plant development and stress resistance. However, studies on B-RRs in tomato are limited. In this study, we conducted a comprehensive analysis of the B-RRs gene family in tomato. A total of 10 genes encoding B-RRs transcription factors (named as SlRR1 to SlRR10) were identified. We analyzed the structure, chromosomal localization, phylogeny, protein motifs, and expression levels of these B-RRs genes. Gene structure analysis revealed that the B-RRs genes in tomato possess between 4-11 exons and 4-12 introns. These genes are distributed across eight chromosomes. Phylogenetic tree analysis classified the B-RRs genes into three distinct subfamilies: subfamily I contains 6 genes that share five motifs, subfamily II includes 1 gene that shares three motifs, and subfamily III comprises 3 genes that share four motifs. Expression analysis demonstrated that SlRR1, SlRR2, and SlRR5 are highly expressed in the vegetative meristem, while SlRR3, SlRR4, and SlRR9 exhibit high expression levels in the roots. SlRR7 was predominantly expressed in the fruits, whereas SlRR6, SlRR8, and SlRR10 show low expression or are undetectable in all tissues. Cis-element analysis revealed the presence of drought and abscisic acid (ABA) response elements in the promoters of the B-RRs genes. Correspondingly, their expression was significantly suppressed by both Polyethylene glycol (PEG) -induced drought stress and exogenous ABA treatment. Given the established antagonism between cytokinin and ABA, our findings suggest that tomato B-RRs may not only play a role in cytokinin signaling but also potentially serve as key nodes in the crosstalk between cytokinin and ABA pathways during drought stress responses. These findings indicate that the B-RRs genes in tomato are vital for plant growth, development, and stress resistance.