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

Pc-2基因不仅对燕麦冠锈病具有抗性，而且对小麦白粉病和黄曲霉毒素敏感。现已发现，Victorin可以作为燕麦中植物抗菌素的特异性诱导子。因此，本研究采用的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良好模式系统。通过将基因组文库与从Victorin处理组中提取的mRNA杂交，对仅在处理组中激活的特定基因进行差异筛选。在处理组中检测到几个诱导基因。从维生素C处理后的细胞中提取总m-RNA，提取总m-RNA，制备c DNA。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)基因的Northern印迹杂交表明，维克托林可激活PAL基因，但不能激活CHS和CHI基因。PAL的激活模式与燕麦铝蛋白的积累是平行的。维克托林处理诱导了几丁质酶活性的提高，只有维克托林处理的叶片中才有几丁质酶。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.