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item Cui, Yunxing
item Bell, Alois - Al
item Joost, Oscar
item Magill, Clint

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: The cotton plant responds to microbial infections by synthesizing chemicals that kill or retard the development of the invading microorganisms. When these reactions occur, primarily after contact is made with the microorganism, they are called active defense responses. We used various molecular techniques to study the potential active defense responses of the cotton plant to a fungal wilt pathogen. The results give us a better understanding of the biochemical mechanisms used by cotton to defend itself against disease. Further, the results can be used to increase resistance to disease.

Technical Abstract: Induction of genes needed to synthesize terpenoid compounds that have antifungal activity has previously been demonstrated to occur earlier in SBSI, a wilt resistant cotton cultivar than in the susceptible cultivar, Rowden, Here, we have used cloned probes to test the same cultivars for induced expression of genes from other known defense response pathways. The time course of mRNA appearance was followed for up to four days in stele tissues of control plants and in plants inoculated with conidia of the wilt pathogen, Verticillium dahliae. Among genes that code for enzymes in the phenylpropanoid defense pathway, phenylalanine ammonialyase mRNA was constitutively expressed. Levels of mRNA transcripts coding for chalcone synthase, an enzyme required for flavonoids biosynthesis and for caffeic-O-methyltransferase, an enzyme used in synthesis of lignin were greatly elevated in inoculated plants as compared to water treated controls. Greater and/or earlier initial response was detected in the wilt resistant cultivar than in the susceptible cultivar. Among genes coding for enzymes that can degrade fungal cell walls, equivalent levels of Beta-1,3 glucanase mRNA were present in both fungal and water-treated plants. Chitinase mRNA synthesis was strongly induced in inoculated plants. Levels of message continued to increase in Rowden, but diminished rapidly after 48-60 hours in SBSI.