State Key Lab of Plant Genomics, Institute of Genetics and Developmental Biology, Innovative Academy of Seed Design, Chinese Academy of Sciences, Beijing 100101, China.
College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
Plant Cell. 2022 Oct 27;34(11):4366-4387. doi: 10.1093/plcell/koac250.
Ethylene plays essential roles in adaptive growth of rice (Oryza sativa). Understanding of the crosstalk between ethylene and auxin (Aux) is limited in rice. Here, from an analysis of the root-specific ethylene-insensitive rice mutant mao hu zi 10 (mhz10), we identified the tryptophan aminotransferase (TAR) MHZ10/OsTAR2, which catalyzes the key step in indole-3-pyruvic acid-dependent Aux biosynthesis. Genetically, OsTAR2 acts downstream of ethylene signaling in root ethylene responses. ETHYLENE INSENSITIVE3 like1 (OsEIL1) directly activated OsTAR2 expression. Surprisingly, ethylene induction of OsTAR2 expression still required the Aux pathway. We also show that Os indole-3-acetic acid (IAA)1/9 and OsIAA21/31 physically interact with OsEIL1 and show promotive and repressive effects on OsEIL1-activated OsTAR2 promoter activity, respectively. These effects likely depend on their EAR motif-mediated histone acetylation/deacetylation modification. The special promoting activity of OsIAA1/9 on OsEIL1 may require both the EAR motifs and the flanking sequences for recruitment of histone acetyltransferase. The repressors OsIAA21/31 exhibit earlier degradation upon ethylene treatment than the activators OsIAA1/9 in a TIR1/AFB-dependent manner, allowing OsEIL1 activation by activators OsIAA1/9 for OsTAR2 expression and signal amplification. This study reveals a positive feedback regulation of ethylene signaling by Aux biosynthesis and highlights the crosstalk between ethylene and Aux pathways at a previously underappreciated level for root growth regulation in rice.
乙烯在水稻（Oryza sativa）的适应性生长中发挥着重要作用。然而，人们对乙烯与生长素（Auxin）之间的相互作用在水稻中的理解还很有限。在这里，我们通过对根特异性乙烯不敏感水稻突变体 mao hu zi 10（mhz10）的分析，鉴定了色氨酸转氨酶（TAR）MHZ10/OsTAR2，该酶催化吲哚-3-丙酮酸依赖的Aux生物合成中的关键步骤。遗传上，OsTAR2在根中乙烯信号转导下游发挥作用。ETHYLENE INSENSITIVE3 like1（OsEIL1）直接激活 OsTAR2 的表达。令人惊讶的是，乙烯诱导 OsTAR2 表达仍然需要Aux 途径。我们还表明，Os 吲哚-3-乙酸（IAA）1/9 和 OsIAA21/31 与 OsEIL1 物理相互作用，并分别对 OsEIL1 激活的 OsTAR2 启动子活性表现出促进和抑制作用，这些作用可能依赖于它们的 EAR 基序介导的组蛋白乙酰化/去乙酰化修饰。OsIAA1/9 对 OsEIL1 的特殊促进活性可能需要 EAR 基序和侧翼序列来招募组蛋白乙酰转移酶。与激活剂 OsIAA1/9 相比，抑制子 OsIAA21/31 在 TIR1/AFB 依赖的方式下，乙烯处理后会更早降解，从而允许激活剂 OsIAA1/9 激活 OsEIL1 以表达 OsTAR2 并放大信号。这项研究揭示了 Aux 生物合成对乙烯信号的正反馈调节，并强调了在根生长调控中，乙烯和 Aux 途径之间的相互作用以前被低估了。
