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.