Expression of potential defense response genes in cotton

Induction of genes needed to synthesize terpenoid compounds that have antif ungal activity has previously been demonstrated to occur earlier in SBSI, a wilt resistant cotton cultivar, than in the susceptible cultivar: Rowden. In this study we have used cloned probes to lest the same cultivars for ind uced expression of genes from other known defense response pathways. The ti me course of mRNA appearance was followed for up to 4 days in stele tissues of control plants and in plants inoculated with conidia of the wilt pathog en, Verticillium dahliae. Among genes that code for enzymes in the phenylpr opanoid defense pathway, phenylalanine ammonia-lyase mRNA was constitutivel y expressed. Levels of mRNA transcripts coding for chalcone synthase, an en zyme required for flavonoid biosynthesis, and for caffeic-O-methyltransfera se, an enzyme used in synthesis of lignin, were greatly elevated in inocula ted plants as compared to water treated controls. Greater and/or earlier in itial response was detected in the wilt resistant cultivar than in the susc eptible cultivar. Among genes coding for enzymes that can degrade fungal ce ll walls, equivalent levels of beta-1,3 glucanase mRNA were present in both fungal and water-treated plants. Chitinase mRNA synthesis was strongly ind uced in inoculated plants. Levels of message continued to increase in Rowde n, hut diminished rapidly after 48-60 h in SBSI. (C) 2000 Academic Press.