UV-B signaling in maize Transcriptomic and metabolomic studies at different irradiation times

Plants have evolved adaptations to environmental factors, including UV-B present in solar radiation. Deployment of specific adaptive phenotypes to avoid or repair UV-B damage requires physiological and developmental acclimation to variable UV-B fluence. To gain a better understanding of the events in UV-B acclimation, we have analyzed a 5 min to 6 h time course of transcriptome and metabolome responses in irradiated and shielded leaves and in immature maize ears to unravel the systemic physiological and developmental responses in exposed and shielded organs. Within 10 min of UV-B exposure, transcripts are changed not only in irradiated leaves, but also in shielded tissues. The number of UVB- regulated transcripts rapidly increases with exposure length. Interestingly, after 10 min of exposure, the overlap in transcriptome changes in irradiated and shielded organs is significant; while, after 6 h of UV-B, most transcripts are specific for each tissue under study. We suggest that early events in all tissues may be elicited by common signaling pathways, while at longer exposure times responses become more organ-specific. Our working hypothesis is that mobile signaling molecules are generated in irradiated organs to elicit the initial responses. We found several metabolites that rapidly change after different treatments during the timecourse; myoinositol is one candidate metabolite based on its rapid modulation in all organs. There is also support from RNA profiling: after 1 h UV-B, transcripts for myoinositol-1phosphate synthase are decreased in both irradiated and shielded leaves suggesting downregulation of biogenesis.