State Key Laboratory for Crop Stress Resistance and High-Efficiency Production/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, 712100 Shaanxi, China.
Plant Cell. 2024 Feb 26;36(3):585-604. doi: 10.1093/plcell/koad297.
Auxin plays important roles throughout plant growth and development. However, the mechanisms of auxin regulation of plant structure are poorly understood. In this study, we identified a transcription factor (TF) of the BARLEY B RECOMBINANT/BASIC PENTACYSTEINE (BBR/BPC) family in apple (Malus × domestica), MdBPC2. It was highly expressed in dwarfing rootstocks, and it negatively regulated auxin biosynthesis. Overexpression of MdBPC2 in apple decreased plant height, altered leaf morphology, and inhibited root system development. These phenotypes were due to reduced auxin levels and were restored reversed after exogenous indole acetic acid (IAA) treatment. Silencing of MdBPC2 alone had no obvious phenotypic effect, while silencing both Class I and Class II BPCs in apple significantly increased auxin content in plants. Biochemical analysis demonstrated that MdBPC2 directly bound to the GAGA-rich element in the promoters of the auxin synthesis genes MdYUC2a and MdYUC6b, inhibiting their transcription and reducing auxin accumulation in MdBPC2 overexpression lines. Further studies established that MdBPC2 interacted with the polycomb group (PcG) protein LIKE HETEROCHROMATIN PROTEIN 1 (LHP1) to inhibit MdYUC2a and MdYUC6b expression via methylation of histone 3 lysine 27 (H3K27me3). Silencing MdLHP1 reversed the negative effect of MdBPC2 on auxin accumulation. Our results reveal a dwarfing mechanism in perennial woody plants involving control of auxin biosynthesis by a BPC transcription factor, suggesting its use for genetic improvement of apple rootstock.
生长素在植物生长发育的各个阶段都发挥着重要作用。然而，生长素调控植物结构的机制尚不清楚。本研究在苹果（Malus × domestica）中鉴定到一个 BRECOM-BINANT/BASIC PENTACYSTEINE（BBR/BPC）家族的转录因子（TF），即 MdBPC2。该基因在矮化砧木中高度表达，且负调控生长素的生物合成。在苹果中过表达 MdBPC2 会降低植株高度，改变叶片形态，并抑制根系发育。这些表型是由于生长素水平降低所致，外源吲哚乙酸（IAA）处理后表型得到恢复。单独沉默 MdBPC2 没有明显的表型效应，而在苹果中同时沉默 Class I 和 Class II BPCs 则显著增加了植物中的生长素含量。生化分析表明，MdBPC2 直接结合生长素合成基因 MdYUC2a 和 MdYUC6b 启动子中的 GAGA 富含元件，抑制其转录并减少 MdBPC2 过表达系中的生长素积累。进一步的研究表明，MdBPC2 与多梳抑制复合物（PcG）蛋白 LIKE HETEROCHROMATIN PROTEIN 1（LHP1）相互作用，通过组蛋白 3 赖氨酸 27（H3K27me3）的甲基化抑制 MdYUC2a 和 MdYUC6b 的表达。沉默 MdLHP1 逆转了 MdBPC2 对生长素积累的负效应。我们的研究结果揭示了一个在多年生木本植物中控制生长素生物合成的矮化机制，该机制涉及到 BPC 转录因子的作用，这为苹果砧木的遗传改良提供了一个潜在的途径。
