Plant breeders have long identified and cultivated disease-resistant varieties. A research team at the University of California, Riverside has now revealed a new molecular mechanism for resistance and susceptibility to a common fungus that causes wilt in susceptible tomato plants.
The researchers started with two closely related tomato cultivars: “Moneymaker” is susceptible to the wilting fungus Fusarium oxysporum whereas “Motelle” is resistant. In their search for what makes the two different, the researchers focused on microRNAs, small molecules that act by regulating the expression of a variety of genes, including genes involved in plant immunity.
They treated roots from the two cultivars with water or with a solution containing F. oxysporum and looked for microRNAs that were increased in response to the fungus in Moneymaker (where they would inhibit resistance genes) or decreased in Motelle (where they would allow expression of resistance genes). They identified two candidate microRNAs whose levels went down in Motelle after treatment with the fungus.
Because microRNAs inhibit their targets by binding to them, computer searches can find target genes with complementary sequences. Such a search for targets of the two microRNAs identified four candidates in the tomato genome, and all four resembled known plant resistance genes.
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