Role of humidity and light in the initial stage of Arabidopsis-Pseudomonas interaction
S. PANCHAL (1), M. Melotto (1). (1) University of Texas-Arlington, Arlington, TX, U.S.A.
Environmental conditions play a major role in determining the frequency of disease occurrence as well as disease progression in plants. For instance, many bacterial plant disease outbreaks occur after periods of high humidity and rain. Here, we found that high humidity leads to down-regulation of salicylic acid marker genes, important for plant defense, and up-regulation of the jasmonic acid biosynthesis and signaling in Arabidopsis leaves. A critical step in bacterial infection is entry into the plant interior through wounds or natural openings, such as stomata. Recent studies have shown that stomatal closure is an integral part of the plant immune response to reduce pathogen invasion. We found that high humidity can effectively compromise stomatal immunity in both common bean and <i>Arabidopsis</i>. In <i>Arabidopsis</i>, this occurs in a COI1-independent manner. Conversely, periods of darkness are effective in decreasing pathogen penetration into leaves as most stomata are closed. However, we found that coronatine biosynthesis is activated on the leaf surface irrespective of light conditions, thus facilitating infection. We conclude that a well-known disease-promoting environmental condition, high humidity, acts in part by suppressing immunity and virulence factors, such as coronatine, appear to provide epidemiological advantages to ensure bacterial penetration through stomata even when environmental conditions (darkness and insufficient humidity) favor stomatal immunity.
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