Ethylene plays important roles in plant growth and development. Regulation of its signaling is largely unclear especially in crops such as rice. Here, from analysis of an ethylene insensitive mutant mhz11, we identified a GDSL lipase MHZ11 which modulates ethylene signaling in rice roots. MHZ11 is localized to the ER membrane and has acyl-hydrolyzing activity. This activity affects the homeostasis of sterols in rice roots and is required for root ethylene response. MHZ11 overexpression caused constitutive ethylene response in roots. Genetically, MHZ11 acts at the ethylene receptor OsERS2 upstream of OsCTR2 and OsEIN2. MHZ11 mutation maintains more OsCTR2 in phosphorylated form whereas MHZ11 overexpression promotes ethylene inhibition of OsCTR2 phosphorylation. MHZ11 co-localized with the ethylene receptor OsERS2, and its effect on OsCTR2 phosphorylation requires ethylene perception and signaling initiation. mhz11 mutant has over-accumulated sterols. Blocking sterol biosynthesis partially rescued mhz11 ethylene response likely by reducing receptor-OsCTR2 interaction and OsCTR2 phosphorylation. We propose that MHZ11 works to reduce sterol level to impair receptor-OsCTR2 interaction and OsCTR2 phosphorylation for triggering of signaling upon ethylene treatment. Our study reveals a previously unidentified mechanism by which MHZ11 participates in ethylene signaling for regulation of root growth in rice.

乙烯在植物生长发育中起重要作用。其信号的调节在很大程度上尚不清楚，尤其是在水稻等农作物中。在这里，从对乙烯不敏感的突变体mhz11的分析中，我们发现了一种GDSL脂肪酶MHZ11，它可以调节水稻根中的乙烯信号传导。MHZ11位于ER膜上，具有酰基水解活性。该活性影响稻米根中固醇的稳态，是根乙烯反应所必需的。MHZ11过表达引起根的本构乙烯反应。从基因上讲，MHZ11作用于OsCTR2和OsEIN2上游的乙烯受体OsERS2。MHZ11突变以磷酸化形式维持更多的OsCTR2，而MHZ11过表达促进乙烯对OsCTR2磷酸化的抑制。MHZ11与乙烯受体OsERS2共定位，其对OsCTR2磷酸化的影响需要乙烯感知和信号启动。mhz11突变体的甾醇含量过高。阻断固醇的生物合成可能通过减少受体-OsCTR2相互作用和OsCTR2磷酸化来部分挽救mhz11乙烯反应。我们建议MHZ11降低胆固醇水平以损害受体-OsCTR2相互作用和OsCTR2磷酸化，从而在乙烯处理后触发信号传导。我们的研究揭示了MHZ11参与乙烯信号调节水稻根系生长的机制尚未明了。我们建议MHZ11降低胆固醇水平以损害受体-OsCTR2相互作用和OsCTR2磷酸化，从而在乙烯处理后触发信号传导。我们的研究揭示了MHZ11参与乙烯信号调节水稻根系生长的机制尚未明了。我们建议MHZ11降低胆固醇水平以损害受体-OsCTR2相互作用和OsCTR2磷酸化，从而在乙烯处理后触发信号传导。我们的研究揭示了MHZ11参与乙烯信号调节水稻根系生长的机制尚未明了。