Table_3_MdJa2 Participates in the Brassinosteroid Signaling Pathway to Regulate the Synthesis of Anthocyanin and Proanthocyanidin in Red-Fleshed Apple.XLSX

Anthocyanin and proanthocyanidin play important roles in plant secondary metabolism. Although previous studies identified many transcription factors involved in anthocyanin and proanthocyanidin synthesis, the effects of MADS-box transcription factors are unclear in apple. Brassinosteroids (BRs) are steroid hormones that affect plant flavonoid biosynthesis, but the underlying regulatory mechanism is not yet well established. In this study, we identified a MADS-box transcription factor, MdJa2, which contained a highly conserved MADS-box domain and belonged to the STMADS11 subfamily. Additionally, MdJa2 was responsive to BR signal, and the overexpression of MdJa2 inhibited the synthesis of anthocyanin and proanthocyanidin. The silencing of MdJa2 in “Orin” calli promoted anthocyanin and proanthocyanidin accumulations. Moreover, MdJa2 interacted with MdBZR1. MdJa2 was revealed to independently regulate anthocyanin and proanthocyanidin synthesis pathways. The MdJa2–MdBZR1 complex enhanced the binding of MdJa2 to the promoters of downstream target genes. Our research provides new insights into how MADS-box transcription factors in the BR signaling pathway control the accumulations of anthocyanin and proanthocyanidin in red-fleshed apple.花青素（anthocyanin）与原花青素（proanthocyanidin）在植物次生代谢中发挥重要作用。尽管既往研究已鉴定出诸多参与二者合成的转录因子，但MADS-box转录因子（MADS-box transcription factor）在苹果中的调控效应仍不明确。油菜素甾醇（Brassinosteroids, BRs）作为一类甾体激素，可调控植物类黄酮的生物合成，但其具体调控机制尚未完全阐明。本研究鉴定得到一个MADS-box转录因子MdJa2，其含有高度保守的MADS-box结构域，隶属于STMADS11亚家族。进一步研究发现，MdJa2可响应BR信号，且过表达MdJa2会抑制花青素与原花青素的合成；而在‘奥瑞恩’愈伤组织中沉默MdJa2，则可促进二者的积累。此外，MdJa2可与MdBZR1发生相互作用，且能独立调控花青素与原花青素的合成通路。MdJa2与MdBZR1形成的复合物可增强MdJa2对下游靶基因启动子的结合能力。本研究为解析BR信号通路中MADS-box转录因子如何调控红肉苹果中花青素与原花青素的积累提供了新的视角。