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.

Cloning, characterization and expression of wheat EDR1 (enhanced disease resistance) gene.

To investigate if there is an EDR1 pathway in wheat (Triticum aestivum L.), a pair of degenerate primers was designed according to the cDNAs of Arabidopsis thaliana EDR1 gene and its homologs were used to isolate EDR1 gene homologs from wheat. RT-PCR was conducted on the cDNA template synthesized with RNA of wheat leaves. A 627-bp cDNA fragment representing an EDR1 gene (named as TaEDR1) was isolated (GenBank accession number: AY743662). Subsequently, the 3050-bp full-length cDNA sequence of TaEDR1, which encodes a polypeptide consisting of 959 amino acid residues, was obtained by RACE technique. The amino acid sequence of TaEDR1 and that of barley (Hordeum vulgare) EDR1 (signed as HvEDR1) show 92% identity. There is a highly conserved catalytic domain of serine/threonine protein kinases in the C-terminus of TaEDR1. Because this protein has a putative nuclear localization motif, it probably functions in the nucleus. This study provides the first molecular biological evidence of the presence of an EDR1 homolog in common wheat. The transcription pattern of TaEDR1 was investigated in leaves after inoculation with Blumeria graminis (DC.) E.O. Speer f. sp. tritici Em. Marchal (Bgt) through semi-quantitative RT-PCR (semi-QRT-PCR). The result showed that the transcribing of TaEDR1 was enhanced by Bgt. The expression pattern of the TaEDR1 gene in different tissues showed that it expressed in leaves, stems, spikes and roots. This study suggests that the TaEDR1, a MAP kinase kinase kinase, may function in wheat defense responses.