The Study On Regulating Plant Seed Size And Seed Development By Lectin Receptor-like Kinase LecRK-?.2 In Arabidopsis

As a dicotyledonous model plant,Arabidopsis seed yield is closely related to silique number,seed size and seed number.Under suitable growth conditions,Arabidopsis usually assimilates certain amount of energy by photosynthesis,and the proportion of energy allocated to vegetative and reproductive growth is usually fixed.When affected by environmental factors or regulated by developmental signals,photosynthesis and energy allocation of plants change,which subsequently affect silique number,seed size and seed number,and eventually alter seed yield.For example,seed enlargement usually results in decreased number of silique or seed,and vice versa.However,little is known about the molecular mechanism how plants regulate the proportion of energy allocation between vegetative growth and reproductive output according to environmental changes or extracellular signals.In this study,the molecular mechanism of LecRK-?.2 in regulating yield-related traits and seed development was explored by means of genetics,cell biology,biochemistry and bioinformatics.The main results are as follows.(1)Transcriptome and GUS staining showed that LecRK-?.2 was specifically highly expressed during seed development.This suggests that LecRK-?.2 could play an important role during seed development.(2)The lecrk-?.2 mutants develop smaller seeds,but more siliques and seeds,leading to increased yield.In contrast,the plants overexpressing LecRK-?.2 form bigger seeds,but less siliques and seeds,which keep output undistinguishable from that of WT.This indicates that LecRK-?.2 coordinates silique number,seed size and seed number to determine reproductive output.The genetic data demonstrate that LecRK-?.2 promotes the growth of root,stem and leaf by coordinating the energy allocation of sink and source.(3)The cell observation reveals that LecRK-?.2 promotes cell expansion and cell division in seed coat,and positively regulates embryo and seed size.The qPCR data indicate that LecRK-?.2 positively regulates EXPA15 expression.The reciprocal cross experiment demonstrate that LecRK-?.2 maternally influences seed size.(4)The genetic and biochemical data indicate that LecRK-?.2 acts upstream of MPK6,and coordinates silique number,seed size and seed number to determine seed output by adjusting MPK6 phosphorylation level.Overexpressing LecRK-?.2 results in seed development defects.LecRK-?.2 controls seed development by regulating the phosphorylation levels of MPK6 and MPK3 in order.In addition,LecRK-?.2 regulates the accumulation of storage protein and carbohydrate in seeds.(5)Yeast two hybrid assays show that LecRK-?.2 formed homodimer or heterodimer with LecRK-?.1,suggesting that LecRK-?.2 and LecRK-?.1 could play similar roles to regulate plant growth and development.The 26 interacting proteins with LecRK-?.2 were identified by Co-IP/MS and Y2H experiments.Several binding sites of transcription factors and micro RNA in the promoter and 5'UTR region of LecRK-?.2 were predicted.The signaling network of LecRK-?.2 regulating plant growth and development has been preliminarily characterized.(6)The results of homologous modelling,ligands screen and molecular docking reveal that D-mannose and D-Glucose may be the ligands of LecRK-?.2.Gus staining and seed germination experiments reveal that mannose inhibits seed germination,while glucose relieves the inhibitory effect.Mannose and glucose treatment induced LecRK-?.2-GUS expression.Compared with wild type,lecrk-?.2 mutants and overexpression plants were insensitive to mannose treatment at seed germination stage,but hypersensitive to glucose.This suggests that LecRK-?.2 may be a sensor of mannose and glucose.(7)Overexpressing AtLecRK-?.2 in Nipponbare resulted in semi-dwarfed plant and decreased biomass of shoot.Although the number of panicles increased,grain yield was significantly lower than that of WT due to smaller grain size and lower seed setting ratio.This work reveals the molecular mechanism of Arabidopsis LecRK-?.2 in regulating yield-related traits and seed development,and constructs the protein interaction signal network with LecRK-?.2 as the core,and preliminarily explores the mechanism of LecRK-?.2 in regulating mannose/glucose response,and discovers the roles of AtLecRK-?.2 in regulating grain size and development in rice.This study lays the solid foundation for further study on organizing plant growth and development by LecRK-?.2.