Cloning, characterization and expression analysis of the receptor-like kinase gene (RLK) in common wheat

To investigate whether homologs of wheat (Triticum aestivum L.) LRK10 gene was expressed in powdery mildew-resistant lines after inoculation with Blumeria graminis f. sp. tritici, one degenerate primer for 5'-RACE was designed according to the 6th kinase subdomain of LRK10 and other plant kinases. 5'-RACE was performed with the template cDNA synthesized with RNA extracted from seedling leaves of a powdery mildew-resistant wheat line "99-2439" after inoculation with B. graminis. One 1551 bp cDNA fragment representing a protein kinase gene was obtained (S1125, GenBank accession number: AY584533). Subsequently, a 2255-bp full-length cDNA clone with a complete encoding region (open reading frame, ORF) was obtained by RACE. The clone encodes a polypeptide consisting of 637 amino acid residues. The result of homology search showed that it belongs to a receptor-like kinase gene family in wheat, which was named as wlrk (wheat leaf rust kinase) previously. Similar to LRK10, this protein kinase has five distinct domains: a hydrophobic signal sequence at the amino-terminus, a putative extracellular domain, a transmembrane domain, a highly charged sequence and a serine/threonine kinase domain at the carboxy-terminus, and thus it was named as TaLRK (Triticum aestivum LRK). The expression pattern of TaLRK at transcription level in leaves after B. graminis infection was investigated by semi-quantitative RT-PCR (semi-QRT-PCR), using wheat actin gene as a control. The result showed that the transcription of TaLRK was significantly enhanced by B. graminis infection. The expression pattern of TaLRK in different tissues showed that this new wheat RLK gene was expressed only in green parts of wheat. This study suggests that TaLRK may function in wheat powdery mildew resistance responses.