Molecular cloning of a putative receptor protein kinase gene encoded at the self-incompatibility locus of Brassica oleracea.

Abstract

Self-recognition between pollen and stigma during pollination in Brassica olracea is genetically controlled by the multiallelic self-incompatibility locus (S). We describe the S receptor kinase (SRK) gene, a previously uncaracterize gene that resides at the S locus. The nucleotide sequences of genomic DNA and of cDNAs corresponding to SRK predict a putative transmembrane receptor having serine/threoninespecific protein kinase activity. Its extracellular domain exhibits king homology to the secreted product of the S-locus glycoprotein (SLG) gene and is connected via a single pass trausmembrane domain to a protein kina catalytic center.SRK alleles derived from different S-locus genotypes are highly polymorphic and have apparently evolved in unison with genetically linked alleles of SLW. SRK directs the synthesis of several alternative transcripts, which potentially encode different protein products, and these transcripts were detected exclusively in reproductive organs. The identification of SRK may provide new perspectives into the signal transduction mechanism underlying pollen recognition.Pollination and the subsequent invasive growth of pollen tubes into the female stigmatic and pistil tissues prior to fertilization provide an opportunity to study cell-cell interactions in flowering plants. In crucifers such as Brassica oleracea, self-recognition between pollen and stigma is controlled by the multiallelic self-incompatibility, or S, locus (1). In general, pollen germination and/or tube growth are arrested at the stigma surface if the pollen and stigma are borne by plants having identical S-locus genotypes. This arrest prevents self-fertilization and is termed the self-incompatibility (SI) response. Two related genes have been identified at the S locus by molecular methods (2-4). Of these, only one gene, the S-locus glycoprotein (SLG) gene has been characterized extensively. SLG encodes a secreted glycoprotein that is highly polymorphic in different S-locus genotypes (2) and may therefore be involved in determining the recognition specificity displayed in SI. Furthermore, SLG is expressed in stigmatic papillae (3) and anthers (5, 6), consistent with models for SI in which both pollen and stigma bear recognition determinants derived from the S locus.In this study, we show that the second S-locus-linked gene (4) encodes a putative receptor protein kinase, and we have therefore designated it SRK, for S receptor kinase.t Its structure is similar to that predicted in a recently described maize root cDNA clone, ZmPKJ (7), and is analogous to the growth factor receptor tyrosine kinases in animals. The putative ligand-binding domain is homologous to SLG and displays genotype-specific sequence polymorphisms that parallel those of SLG. SRK transcripts were detected only in the male and female reproductive organs, thus showing a pattern of expression similar to that of SLG. These findings offer foundation to the hypothesis that SI is mediated by receptor-ligand interactions between pollen and pistil and provide a ...

Molecular cloning of a new receptor‐like kinase gene encoded at the Lr10 disease resistance locus of wheat

“…These residues are boxed in the LRK1O and SRK6 (Stein et al, 1991) or any other proteins in genome databases and therefore represents a new type of extracellular domain. A very limited homology with S-domain receptor kinases was detected: in a segment of 12 amino acids, eight residues are conserved in S-locus glycoproteins and receptor-like kinases having an extracellular S-domain (Walker, 1994).…”

CHRK1, a Chitinase-Related Receptor-Like Kinase in Tobacco

“…1B). This domain is closely related to plant RLKs, including ARK3 from Arabidopsis (50% identity; Dwyer et al, 1994), SRK6 from Brassica oleracea (47% identity; Stein et al, 1991), and PR5K from Arabidopsis (36% identity; Wang et al, 1996).…”

“…The deduced amino acid sequence of the CD of CHRK1 was aligned with the sequences from class V chitinase (CHIV) from tobacco (Melchers et al, 1994) and chitinase A1 (CHIA) from B. circulans (Watanabe et al, 1990). The predicted KD was aligned with the KD of the plant RLKs, SRK6 of Brassica (Stein et al, 1991), and ARK3 (Dwyer et al, 1994) and PR5K (Wang et al, 1996) of Arabidopsis. The number on the right indicates the amino acid residues.…”

Self-Incompatibility System of Ipomoea trifida, a Wild-Type Sweet Potato

“…Because I. trifi da has the same genetic SI system as Brassica species, it might be expected that products of genes homologous to SLG or SRK would be present in the reproductive tissues of I. trifi da. SRK is known as a female S -gene (Stein et al 1991 ;Takasaki et al 2000 ), and SLG is an S -gene-related gene in Brassica (Kandasamy et al 1989 ). Ipomoea secreted glycoprotein genes ( ISG1 , -2 , and -3 ) were isolated from a mature stigma cDNA library, and the sequences of these genes showed structural similarities to Brassica SLGs.…”