Modulation of jasmonate sensitivity by reflection signals. A phytochrome answer to de dilemma of plants

BALLARÉ CL; MORENO JE

Merida, Mexico

Simposio; Plant Biology 2008, ASPB; 2008

ASPB

Abs # M1104: Modulation of jasmonate sensitivity by reflection signals. A phytochrome answer to the dilemma of plants Presenter: Ballare, Carlos L.       Contact Presenter Authors Ballare, Carlos L. (A)   Moreno, Javier E (A)   Affiliations: (A): IFEVA, Universidad de Buenos Aires One of the most widespread responses of plants to the attack of herbivore insects is the activation of chemical defenses. Previous studies have shown that plants down-regulate the expression of chemical defenses when they perceive an increased risk of competition with neighboring plants. In the experiments reported here we provide evidence that this down-regulation of defense is mediated, at least in part, by an effect of phytochrome on the sensitivity of the plant to jasmonic acid (JA). Plants exposed to supplementary far-red radiation (FR), a competition signal perceived by phytochrome, had reduced levels of defenses compared to control plants grown without FR supplementation. This was demonstrated by measurements of phenolic compounds and direct evaluations of plant tissue quality using bioassays with Spodoptera frugiperdalarvae. Several JA-inducible genes were up-regulated in response to feeding by S. frugiperda caterpillars in control plants, but this up-regulation was absent in plants exposed to FR radiation. Exogenous application of MeJA caused an increase in the levels of phenolic compounds and up-regulated genes putatively involved in JA signaling and response. When the plants were exposed to reflected FR, the phenolic response was abolished and the up-regulation of gene expression was cancelled or greatly reduced in the case of ERF1, a regulator of JA- and ethylene-inducible genes, and PDF1.2 and HEL, two markers of JA response. The JA-induced expression of MYC2 and VSP1, in contrast, was not affected by FR. We conclude that selective de-sensitization to jasmonates is the mechanism whereby the plant switches it resource allocation strategy, from defense to shade avoidance, in response to phytochrome-perceived signals of intense future competition.