SERKs Regulate Divisions Of The Vascular Precursors And The Ground Tissue Stem Cells During Embryo Development In Arabidopsis Thaliana

Current studies show that membrane-anchored receptor-like protein kinases regulate plant growth,development and defense response.The SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE(SERK)family belongs to the second subgroup of leucine-rich repeat receptor-like kinases(LRR-RLKs)in Arabidopsis thaliana.SERKs function as co-receptors and bind to different receptors to regulate different biological processes,such as brassinosteroid signal transduction,anther cell differentiation,stomata patterning,plant innate immunity response,vascular development,floral organ abscission,and so on.When our group studied the mechanism that SERKs regulate BR signaling,it was revealed that seedlings and seeds of two independent serk1 serk2 bak1 triple mutants exhibit developmental defects.As we known,the morphology of the seed is closely related to embryo development,a process that is highly organized and predictable in model plant Arabidopsis thaliana.In this study,we observed embryo development of wild-type and serk1-8 serk2-1 bak1-4 triple mutants by DIC microscopy and confocal laser scanning microscopy in detail.The results showed that fewer vascular tissue,cortical cel,endodermal cell and epidermis cell are generated in the embryo of serk1-8 serk2-1 bak1-4 triple mutants.It has been shown that the divisions of vascular precursors and ground tissue stem cels plays an important role in embryo development in Arabidopsis thaliana: the vascular precursors undergo oriented division to generate the vascular tissue;the ground tissue stem cels divide to generate new ground tissue stem cels and daughter cels,the daughter cels undergo asymmetrical division and produce endodermal cels and cortical cels.Compared with wild type,the first transverse division of the vascular precursors in serk1-8 serk2-1 bak1-4 mid-globular embryos is abnormally altered to a longitudinal division.The ground tissue stem cels in serk1-8 serk2-1 bak1-4 earlyheart embryos undergo a longitudinal division and probably differentiate into cortical cels and endodermal cels.The altered divisions of the vascular precursors and the ground tissue stem cels in serk1-8 serk2-1 bak1-4 embryo impaired development of vascular tissue,cortical cels and endodermal cels.We further found that yda-Y295 and mkk4-18 mkk5-18 embryos exhibited a phenotype similar to that of serk1-8 serk2-1 bak1-4 embryos.The vascular tissue cell identity had changed in serk1-8 serk2-1 bak1-4,yda-Y295 and mkk4-18 mkk5-18 embryos.The serk1-8 serk2-1 bak1-4 embryo defects can be partially rescued by constitutively activated YDA and MKK5,especially abnormal division of the ground tissue stem cels.Our study suggests that SERK-mediated signals are likely transduced via the YDA-MKK4/5 cascade to regulate division patterns of the vascular precursors and the ground tissue stem cels during Arabidopsis thaliana embryogenesis.Revealing the mechanism that SERKs regulate divisions of the vascular precursors and the ground tissue stem cels in Arabidopsis thaliana facilitates to further understand the process of embryo development in dicots.