<scp>YGL9</scp> mediates <scp>LHC</scp> assembly by regulating <scp>LHCPs</scp> transport and chlorophyll synthesis in rice

LHC assembly is a fundamental process in forming a peripheral antenna system, which has a significant impact on photosynthesis. However, the molecular mechanism of the LHC assembly still needs to be further investigated in monocotyledonous plants. Here, we identified a bifunctional protein YGL9 in rice, a homolog of cpSRP43 in Arabidopsis, mediates LHC assembly by simultaneously regulating LHCPs transport and chlorophyll synthesis. Mutation of YGL9 exhibits a yellow-green leaf phenotype, with reduced LHCPs contents, impaired photosystem activity and reduced chlorophyll content. YGL9 interacts with cpSRP54 forming the cpSRP complex that transport LHCPs, and YGL9 also interacts with and stabilizes OsGUN4, which is an activator of MgCh and participates in the regulation of chlorophyll synthesis, to synergistically participate in chlorophyll synthesis. Further, genetic evidence demonstrates that YGL9 functions in the same pathway as cpSRP54 and OsGUN4 to regulate LHCPs transport and chlorophyll synthesis. Thus, our study reveals a cross-relationship between LHCPs transport and chlorophyll synthesis, and provides new insights into the LHC assembly process in monocotyledonous plants.