Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBioscience, La Trobe University, Bundoora, Melbourne, VIC 3086, Australia.
Plant Cell Physiol. 2020 May 1;61(5):1005-1018. doi: 10.1093/pcp/pcaa027.
MYB-bHLH-WDR (MBW) transcription factor (TF) complexes regulate Arabidopsis seed coat development including mucilage and tannin biosynthesis. The R2R3 MYBs MYB5, MYB23 and TRANSPARENT TESTA2 (TT2) participate in the MBW complexes with the WD-repeat protein TRANSPARENT TESTA GLABRA1 (TTG1). These complexes regulate GLABRA2 (GL2) and TTG2 expression in developing seeds. Microarray transcriptome analysis of ttg1-1- and wild-type (Ler) developing seeds identified 246 TTG1-regulated genes, which include all known metabolic genes of the tannin biosynthetic pathway. The first detailed TTG1-dependent metabolic pathways could be proposed for the biosynthesis of mucilage, jasmonic acid (JA) and cuticle including wax ester in developing seeds. We also assigned many known and previously uncharacterized genes to the activation/inactivation of hormones, plant immunity and nutrient transport. The promoters of six cuticle pathway genes were active in developing seeds. Expression of 11 genes was determined in the developing seeds of the combinatorial mutants of MYB5, MYB23 and TT2, and in the combinatorial mutants of GL2, HOMEODOMAIN GLABROUS2 (HDG2) and TTG2. These six TFs positively co-regulated the expression of four repressor genes while three of the six TFs repressed the wax biosynthesis genes examined, suggesting that the three TFs upregulate the expression of these repressor genes, which, in turn, repress the wax biosynthesis genes. Chromatin immunoprecipitation analysis identified 21 genes directly regulated by MYB5 including GL2, HDG2, TTG2, four repressor genes and various metabolic genes. We propose a multi-tiered regulatory mechanism by which MBWs regulate tannin, mucilage, JA and cuticle biosynthetic pathways.
MYB-bHLH-WDR（MBW）转录因子（TF）复合物调节拟南芥种皮的发育，包括粘液和单宁生物合成。R2R3 MYB 蛋白 MYB5、MYB23 和 TRANSPARENT TESTA GLABRA1（TTG1）与 WD 重复蛋白 TRANSPARENT TESTA GLABRA2（TTG2）一起参与 MBW 复合物。这些复合物在发育中的种子中调节 GLABRA2（GL2）和 TTG2 的表达。ttg1-1-和野生型（Ler）发育中的种子的微阵列转录组分析确定了 246 个 TTG1 调节的基因，其中包括单宁生物合成途径的所有已知代谢基因。可以提出第一个详细的 TTG1 依赖的代谢途径，用于粘液、茉莉酸（JA）和包括发育种子中蜡酯在内的角质层的生物合成。我们还将许多已知和以前未表征的基因分配给激素、植物免疫和养分运输的激活/失活。六种角质层途径基因的启动子在发育中的种子中具有活性。在 MYB5、MYB23 和 TT2 的组合突变体以及 GL2、HOMEODOMAIN GLABROUS2（HDG2）和 TTG2 的组合突变体的发育种子中测定了 11 个基因的表达。这六个 TF 正向共调节四个抑制基因的表达，而这六个 TF 中的三个抑制了检查的蜡生物合成基因，这表明这三个 TF 上调了这些抑制基因的表达，反过来，抑制了蜡生物合成基因的表达。染色质免疫沉淀分析鉴定了 21 个直接受 MYB5 调节的基因，包括 GL2、HDG2、TTG2、四个抑制基因和各种代谢基因。我们提出了一个多层次的调控机制，MBW 调节单宁、粘液、JA 和角质层生物合成途径。
