Localization And Functional Analysis Of Rice Receptor-like Kinase-OsAPRLK1

High salinity is a common abiotic stress condition that adversely affects plant growth and crop production. Understanding the mechanisms of plants response to salt stress is very instructional for improving plant salt tolerance, especially improving the survival ability and production of crops in high salinity land. At present, studies about the mechanisms of signal transduction of plants response to salt stress are more concentrated on the identification of signal components in cytoplasm and membrane and have some progresses but short for the research of apoplast in stress response. By the development of studies and more peptide signals have been found, apoplast was proved to be not only the barrier between environment and protoplast but also carry out multiple functions in plant development and stress response.The apoplast receptor like kinase OsAPRLK1 in this paper was an up-regulated salt response gene that found in two-dimensional electrophoresis (2-DE) and mass spectrometry analysis of apoplast proteins induced by salt stress in rice root. The results of bioinformatics analysis indicated the OsAPRLK1, which annoted a putative RLK, contain only extracellular domain except for transmembrane domain and kinase domain in fact. With a putative N-terminal signal peptide, OsAPRLK1 protein may act as a secertroy protain. The trait of OsAPRLK1 is two DUF26 domains in its protein structure which belong to one of a large plant kinase family. The function analysis of DUF26 proteins was mainly concentrated on pathogen defense reponse and little about the response in abiotic stress. The analysis of OsAPRLK1 promoter structure showed that there were kinds of cis-act elements response to stress which suggested its function in response to abiotic stress.In this paper, the subcellular localization, expression pattern and functions of OsAPRLK1 have been analysised. The subcellular localization of OsAPRLK1-YFP fusion protein indicated the distribution not only in cytoplast and plasma membrane but also in the apoplast area after plasmolysis, which proved to be a secertory protein that plays a role in extracellular area. Promoter-Gus experiment showed OsAPRLK1 expressed in kinds of tissues from young plant to mature stage, especially in seedlings. According to the results of Semi-quantitive RT-PCR, Real-time PCR and Western blot, we detected the up-regulated expression of OsAPRLK1 in transcript and translate level under salt stress. Because of the decreased expression of OsAPRLK1, the RNAi homozygotes have improved salt tolerance in salt stress experiments. We screened a cDNA library in yeast two hybrid systems by a bait of OsAPRLK1 CDs and found four candidate proteins interacted with the bait. One of these proteins is a universal stress protein (USP). The CDs of this gene has been cloned and retest the interaction with OsAPRLK1 in yeast.For the first time, these results reveal the function of a putative apoplast protein OsAPRLK1 in response to salt stress. Knockdown its expression level leads to increased salt torrence of transgenic rice. This indicated the regulation of apoplast during initial phase in salt stress response, and these results will enlarge our knowledge about the function of apoplast proteins and start a new approach in studies of plant stress resistant mechanism.