Han F, Kleinhofs A, Kilian A, Ullrich S E
Department of Crop and Soil Sciences, Washington State University, Pullman 99164-6420, USA.
Mol Plant Microbe Interact. 1997 Mar;10(2):234-9. doi: 10.1094/MPMI.1997.10.2.234.
The NADPH-dependent HC-toxin reductase (HCTR), encoded by Hm1 in maize, inactivates HC-toxin produced by the fungus Cochliobolus carbonum, and thus confers resistance to the pathogen. The fact that C. carbonum only infects maize (Zea mays) and is the only species known to produce HC-toxin raises the question: What are the biological functions of HCTR in other plant species? An HCTR-like enzyme may function to detoxify toxins produced by pathogens which infect other plant species (R. B. Meeley, G. S. Johal, S. E. Briggs, and J. D. Walton, Plant Cell, 4:71-77, 1992). Hm1 homolog in rice (Y. Hihara, M. Umeda, C. Hara, Q. Liu, S. Aotsuka, K. Toriyama, and H. Uchimiya, unpublished) and HCTR activity in barley, wheat, oats and sorghum have been reported (R. B. Meeley and J. D. Walton, Plant Physiol. 97:1080-1086, 1993). To investigate the sequence conservation of Hm1 and HCTR in barley and the possible relationship of barley Hm1 homolog to the known disease resistance genes, we cloned and mapped a barley (Hordeum vulgare) Hm1-like gene. A putative full-length cDNA clone, Bhm1-18, was isolated from a cDNA library consisting of mRNA from young leaves, inflorescences, and immature embryos. This 1,297-bp clone encodes 363 amino acids which show great similarity (81.6%) with the amino acid sequence of HM1 in maize. Two loci were mapped to barley molecular marker linkage maps with Bhm1-18 as the probe; locus A (Bhm1A) on the long arm of chromosome 1, and locus B (Bhm1B) on the short arm of chromosome 1 which is syntenic to maize chromosome 9 containing the Hm2 locus. The Bhm1-18 probe hybridized strongly to a Southern blot of a wide range of grass species, indicating high conservation of HCTR at the DNA sequence level among grasses. The HCTR mRNA was detected in barley roots, leaves, inflorescences, and immature embryos. The conservation of the HCTR sequence, together with its expression in other plant species (R. B. Meeley and J. D. Walton, Plant Physiol. 97:1080-1086, 1993), suggest HCTR plays an important functional role in other plant species.
由玉米中的Hm1编码的NADPH依赖性HC毒素还原酶（HCTR）可使真菌炭疽菌产生的HC毒素失活，从而赋予对该病原体的抗性。炭疽菌仅感染玉米（Zea mays）且是已知唯一能产生HC毒素的物种，这一事实引发了一个问题：HCTR在其他植物物种中的生物学功能是什么？一种类似HCTR的酶可能具有使感染其他植物物种的病原体产生的毒素解毒的功能（R. B. 米利、G. S. 乔哈尔、S. E. 布里格斯和J. D. 沃尔顿，《植物细胞》，4:71 - 77，1992年）。已报道了水稻中的Hm1同源物（Y. 日原、M. 梅田、C. 原、Q. 刘、S. 青冢、K. 鸟山和H. 内海，未发表）以及大麦、小麦、燕麦和高粱中的HCTR活性（R. B. 米利和J. D. 沃尔顿，《植物生理学》，97:1080 - 1086，1993年）。为了研究大麦中Hm1和HCTR的序列保守性以及大麦Hm1同源物与已知抗病基因的可能关系，我们克隆并定位了一个大麦（Hordeum vulgare）的Hm1样基因。从一个由幼叶、花序和未成熟胚的mRNA构建的cDNA文库中分离出一个推定的全长cDNA克隆Bhm1 - 18。这个1297 bp的克隆编码363个氨基酸，与玉米中HM1的氨基酸序列具有高度相似性（81.6%）。用Bhm1 - 18作为探针，在大麦分子标记连锁图谱上定位了两个位点；位点A（Bhm1A）位于第1染色体长臂上，位点B（Bhm1B）位于第1染色体短臂上，该短臂与含有Hm2位点的玉米第9染色体同线。Bhm1 - 18探针与多种禾本科物种Southern杂交印迹强烈杂交，表明禾本科植物中HCTR在DNA序列水平上具有高度保守性。在大麦的根、叶、花序和未成熟胚中检测到了HCTR mRNA。HCTR序列的保守性及其在其他植物物种中的表达（R. B. 米利和J. D. 沃尔顿，《植物生理学》，97:1080 - 1086，1993年）表明HCTR在其他植物物种中发挥着重要的功能作用。
