Molecular mechanisms of the expression of cultivar-specific resistance in the crown rust of oats

Pc-2基因不仅对燕麦的冠锈病具有抗性，而且对维多利亚helminthspororium victoria和victorin（一种由病原体产生的宿主特有毒素）敏感。研究发现，维多利可以作为一种特殊的促子，促进燕麦的植物抗毒素阿芬铝蛋白的产生。因此，本研究使用的Pc-2 vs victorin系统是阐明燕麦冠锈病品种特异性抗性分子表达的一个很好的模型系统。建立了携带Pc-2基因的燕麦基因组DNA文库。通过将基因组文库与从victorin处理中提取的mRNA杂交，对仅在处理中激活的特定基因进行差异筛选。处理后，检测到多个诱导基因。从victorin处理的植株中提取总m-RNA制备CDNA。对m-RNA与苯丙氨酸解氨酶（PAL）、查尔酮合成酶（CHS）和查尔酮异构酶（CHI）的dna进行Northern blot杂交，结果表明，victorin可激活PAL基因，而CHS和CHI基因未被激活。PAL的激活模式与avenalumin的积累是平行的。结果表明，维多利菌素处理后，几丁质酶活性明显升高，且只在维多利菌素处理过的叶片中发现一种几丁质酶。燕麦PAL和几丁质酶基因的克隆目前正在进行中。

The Pc-2 gene confers not only resistance in the crown rust of oats, but also the sensitivity to Helminthsporium victoriae and victorin, a host-specific toxin, produced by the patogen. It has been found that victorin can function as a specific elicitor for the production of avenalumin, phytoalexin of oats. Thus, it is considered that the Pc-2 vs victorin system used in the present study is a good model system for elucidation of molecular expression of the cultivar-specific resistance in the crown rust of oats.Genomic DNA library of oats carrying Pc-2 gene was prepared. Differential screening of a specific gene activated only in the treated was conducted by hybridizing the genomic library with mRNA extracted from the victorin-treated. Several induced genes were detected in the treated. CDNA was prepared from total m-RNA extracted from the victorin-treated. Northern blot hybridization of the m-RNA with cDNAs of phenylalanine ammonia-lyase(PAL), chalcone synthetase(CHS) and chalcone isomerase(CHI) indicated that PAL genes were activated by victorin-treatment, but not CHS and CHI genes. The pattern of PAL activation was parallel with the accumulation of avenalumin. It was also found that victorin treatment induced the increase of chitinase activity in the treated and a chitinase was found only in the victorin-treated leaves. Clonings of genes for PAL and chitinase of oats are now in progress.