GASSHO1 and GASSHO2 encoding a putative leucine-rich repeat transmembrane-type receptor kinase are essential for the normal development of the epidermal surface in Arabidopsis embryos

Receptor-like kinases (RLKs) containing leucine-rich repeats (LRRs) act as both signal receptor and signal transducer in ligand-mediated communication between cells. It is believed that many LRR-RLKs are present in the Arabidopsis genome, but the functions of most are unknown. We recently identified Bnms4D-82, an expressed sequence tag (EST) in Brassica napus that encodes an LRR-RLK and is expressed at an early stage of its microspore embryogenesis. To elucidate the function of this gene we used GASSHO1 (GSO1) and GSO2, two Arabidopsis genes with a high degree of homology with Bnms4D-82. The products of transcripts of GSO1 and GSO2 accumulate in parts of the embryo and in seedlings, but not in true leaves. Plants that lacked both GSO1 and GSO2 exhibited pleiotropy, including abnormal bending of embryos, ectopic adhesion between cotyledons, a highly permeable epidermal structure, and an abnormal pattern of distribution of stomata on cotyledons in embryos and seedlings. However, plants homozygous for either gso1-1 or gso2-1 had no visible abnormality. These results suggest that GASSHO genes are essential for the formation of a normal epidermal surface during embryogenesis.