?Impact of UV-B on maize?

VIRGINIA WALBOT; PAULA CASATI

Aix-les-Bains, Francia.

Congreso; 11th Congress of the European Society for Photobiology.; 2005

European Society for Photobiology

Given their sessile growth habit and requirement for sunlight in photosynthesis, land plants are inevitably exposed to UV-B. Plants cope with this environmental stress through various shielding strategies (such as synthesis of sunscreen pigments) and by repair of damage. Using  transcriptome profiling of lines varying in sunscreen pigment content we have confirmed several known UVB stimulated processes and identified new pathways and processes that respond to UV-B radiation in terms of gene expression in a dosage-dependent manner. We have defined gene expression changes in directly irradiated and shielded organs. Translation associated factors are a major class of responsive genes in irradiated tissues, and we demonstrate that UV-B crosslinks specific ribosomal proteins to RNA and propose that new ribosomes must be synthesized to restore protein synthesis capacity. Using maize landraces from high altitudes we have identified acclimations and adaptations to increased UV-B fluence in the natural environment including flavone sunscreen synthesis in leaves and expression of a suite of likely chromatin-associated factors. RNAi knockdown lines for four such chromatin-associated factors exhibit hypersensitivity to UV-B including sunburning and ultimately necrosis. Our long-term goal is to determine how UV-B radiation reactivates silenced Mutator transposons of maize; reactivation occurs in both directly irradiated tissues (where DNA damage occurs) and in fully shielded tissues. Finding chromatin remodeling factors involved in UV-B responses is a clue to the underlying mechanism of transposon activation.