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 YrlO candidate gene （YrlOca） and slow-rusting genes Lr34/Yr18 （hereafter designated as Yrl8） and Fr36. 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 YrlOca and Yr18nn （the resistant haplotype of YrlS）, respectively, but none were positive for the Yr36 marker. Since there is a limited use of the YrlO gene in Chinese wheat, the relatively high frequency of wheat varieties with the YrlOcG marker suggests that the identity of the YrlO 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 Yrl8RH markers. A non-functional allele of Yrl8Rn 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
EDR2 is a negative regulator of the defense response and cell death in Arabidopsis.Loss-of-function of EDR2 leads to enhanced resistance to powdery mildew.To identify new components in the EDR2 signal transduction pathway,mutations that suppress edr2 resistant phenotypes were screened.Three mutants,edts5-1,edts5-2 and edts5-3（edr two suppressor 5）,were identified.The EDTS5 gene was identified by map-based cloning and previously was shown to encode an aminotransferase（ALD1）.Therefore we renamed these three alleles ald1-10,ald1-11 and ald1-12,respectively.Mutations in ALD1 suppressed all edr2-mediated phenotypes,including powdery mildew resistance,programmed cell death and ethylene-induced senescence.Accumulation of hydrogen peroxide in edr2 was also suppressed by ald1 mutation.The expression of defense-related genes was up-regulated in the edr2 mutant,and the up-regulation of those genes in edr2 was suppressed in the edr2/ald1 double mutant.The ald1 single mutant displayed delayed ethylene-induced senescence.In addition,ald1 mutation suppressed edr1-mediated powdery mildew resistance,but could not suppress the edr11edr2 double-mutant phenotype.These data demonstrate that ALD1 plays important roles in edr2-mediated defense responses and senescence,and revealed a crosstalk between ethylene and salicylic acid signaling mediated by ALD1 and EDR2.
Dear Editor, The general way to probe functions of a protein in vivo is to perturb its level and then observe subsequent phe- notypic 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 pro- teins when fused to it. A small synthetic molecule ligand Shield 1 （Shldl） can bind DD and shield it from degrada- tion. The level of DD fused protein can be controlled by adjusting Shldl concentration （Banaszynski et al., 2006）.
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 gh3.5-1DIpad3-1, 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
