Genome-wide characterization of RR gene family members in Zanthoxylum armatum and the subsequent functional characterization of the C-type RR.

Response Regulators (RRs) are crucial regulators in plant development and stress responses, comprising A-type, B-type, C-type, and pseudo-RR subfamilies. However, previous studies have often focused on specific subfamilies, which restricts our understanding of the complete RR gene family. In this study, we conducted a comprehensive analysis of 63 RR members from Zanthoxylum armatum, using phylogenetic relationships, motif composition, cis-acting elements, gene duplication and collinearity analyses. Segmental repeats among ZaRR genes enhanced the various environmental adaptabilities of Z. armatum, and the B-type ZaRR exhibited significant collinearity with the RRs in P. trichocarpa and C. sinensis. Cis-element analysis indicated ZaRRs play a significant role in abiotic stress and phytohormone pathways, particularly in light, drought, cold, abscisic acid (ABA) and salicylic acid (SA) responses. Abundant Ethylene Response Factor (ERF) and reproduction-associated binding sites in ZaRR promoters suggested their roles in stress and reproductive processes. A-type ZaRRs were implicated in plant vegetative and reproductive growth, whereas B-type ZaRRs contributed to both growth and stress responses. C-type ZaRRs were associated with plant reproductive growth, whereas pseudo-RRs may function in plant stress responses, such as water logging, cold, and response to ethylene (ETH), SA, and jasmonic acid (JA). Ectopic expression of ZaRR24, a C-type RR, inhibits growth, induces early flowering, and shortens fruit length in Arabidopsis. ZaRR24 overexpression also affected the expression of A- and B-type RRs, as well as floral meristem and organ identity genes. These findings establish a solid and comprehensive foundation for RR gene research in Z. armatum, and provide a platform for investigating signal transduction in other woody plants.