Wheat stripe rust is a devastating disease in many regions of the world.In wheat,49 resistance genes for stripe rust have been officially documented,but only three genes are cloned,including the race-specific resistance Yr10 candidate gene(Yr10_(CG)) and slow-rusting genes Lr34/Yr18(hereafter designated as Yr18) and Yr36.In this study,we developed gene-specific markers for these genes and used them to screen a collection of 659 wheat accessions,including 485 Chinese cultivars.Thirteen percent and eleven percent of the tested Chinese cultivars were positive for the markers for Yr10_(CG) and Yr18_(RH)(the resistant haplotype of Yr18),respectively,but none were positive for the Yr36 marker.Since there is a limited use of the Yr10 gene in Chinese wheat,the relatively high frequency of wheat varieties with the Yr10_(CG) marker suggests that the identity of the Yr10 gene is unknown.With regards to the Yr18 gene,29%of the tested cultivars that are used in the Middle and Lower Yangtze Valleys' winter wheat zone were positive for Yr18_(RH) markers.A non-functional allele of Yr18_(RH) was identified in 'Mingxian 169',a commonly used susceptible check for studying stripe rust.The data presented here will provide useful information for marker-assisted selection for wheat stripe rust resistance.
Cuiling YuanHui JiangHonggang WangKun LiHeng TangXianbin LiDaolin Fu
Dear Editor, The general way to probe functions of a protein in vivo is to perturb its level and then observe subsequent phenotypic changes.In plants,modulation of protein level is mainly carried out at DNA or RNA level,which is indirect and thus affected by stability of the target protein.Thus,experimental approaches to perturb protein level directly are needed,but still limited in plants.In mammalian cells,a technique to modulate protein level directly has been developed.Engineered destabilizing domain (DD) of the human FKBP12 protein can confer instability to other proteins when fused to it.A small synthetic molecule ligand Shield 1 (Shld1) can bind DD and shield it from degradation.The level of DD fused protein can be controlled by adjusting Shld1 concentration (Banaszynski et a1.,2006).The DD-Shld1 system was further successfully applied in several other species,such as parasites Plasmodium falciparum (Armstrong and Goldberg,2007) and Toxoplasma gondii (Herm-G(o)tz et al.,2007).
Camalexin (3-thiazol-2 -yl-indole) is the major phytoalexin found in Arabidopsis thaliana. Several key intermediates and corresponding enzymes have been identified in camalexin biosynthesis through mutant screening and biochemical experiments. Camalexin is formed when indole-3-acetonitrile (IAN) is catalyzed by the cytochrome P450 monooxygenase CYP71A13. Here, we demonstrate that the Ara- bidopsis GH3.5 protein, a multifunctional acetyl-amido synthetase, is involved in camalexin biosynthesis via conjugating indole-3-carboxylic acid (ICA) and cysteine (Cys) and regulating camalexin biosynthesis genes. Camalexin levels were increased in the activation-tagged mutant gh3.5-1D in both Col-0 and cyp71A13-2 mutant backgrounds after pathogen infection. The recombinant GH3.5 protein catalyzed the conjugation of ICA and Cys to form a possible intermediate indole-3-acyl-cysteinate (ICA(Cys)) in vitro. In support of the in vitro reaction, feeding with ICA and Cys increased camalexin levels in Col-0 and gh3.5-1D. Dihydrocamalexic acid (DHCA), the precursor of camalexin and the substrate for PAD3, was accumulated in gh3.5-1D/pad3-1, suggesting that ICA(Cys) could be an additional precursor of DHCA for camalexin biosynthesis. Furthermore, expression of the major camalexin biosynthesis genes CYP79B2, CYP71A12, CYP71A13 and PAD3 was strongly induced in gh3.5-1D. Our study suggests that GH3.5 is involved in camalexin biosynthesis through direct catalyzation of the formation of ICA(Cys), and upregulation of the major biosynthetic pathway genes.
Mu-Yang WangXue-Ting LiuYing ChenXiao-Jing XuBiao YuShu-Qun ZhangQun LiZu-Hua He
