Histidine kinase MHZ1/OsHK1 interacts with ethylene receptors to regulate root growth in rice

We discovered that MHZ1 positively modulates root ethylene response through analysis of a rice ethylene-response mutant mhz1. MHZ1 encodes the rice histidine kinase OsHK1. MHZ1 autophosphorylates at the conserved histidine and can transfer the phosphoryl signal to response regulator OsRR21 via phosphotransfer proteins OsAHP1/2. This phosphorelay pathway is required for root ethylene response. Ethylene receptor OsERS2, via GAF domain, physically interacts with MHZ1 to inhibit its kinase activity. Our results suggest that MHZ1 mediates ethylene response in a way partially independent of OsEIN2, and is directly inhibited by ethylene receptors. Our study reveals a previously unidentified mechanism of ethylene signaling for root growth regulation.

通过对水稻乙烯响应突变体mhz1的分析，我们发现MHZ1可正向调控根系的乙烯响应。MHZ1编码水稻组氨酸激酶（histidine kinase）OsHK1。MHZ1可在保守组氨酸残基位点发生自磷酸化，并可通过磷酸转移蛋白OsAHP1/2将磷酸信号传递至响应调节因子OsRR21。该磷酸传递级联通路是根系乙烯响应所必需的。乙烯受体OsERS2可通过GAF结构域（GAF domain）与MHZ1发生物理互作，从而抑制其激酶活性。我们的研究结果表明，MHZ1通过一种部分不依赖于OsEIN2的方式介导乙烯响应，且可被乙烯受体直接抑制。本研究揭示了一条此前尚未发现的、调控根系生长的乙烯信号转导机制。