CONICET | Buscador de Institutos y Recursos Humanos

Posttranscriptional mechanisms regulated by microRNAs (miRNAs) play a key role in several developmental processes and responses to environmental changes. In maize, a number of miRNAs were shown to be UV-B regulated by microarray analysis, including, miR172 and miR396. Some of the mRNA targets of miR172, Glossy15 and Indeterminate Spikelet1, and of miR396, GRF1, 3 and 8, show opposite UV-B regulation than the miRNAs. In Arabidopsis, miRNA172 target a set of AP2-like transcription factors (AP2, TOE1, TOE2, TOE3, SNZ and SMZ), most of them act as floral repressors. On the other hand, miRNA396 targets seven GRF transcription factors (GRF1-4 and GRF 7-9), which regulate leaf growth and development. To investigate the UV-B regulation of Arabidopsis thaliana miR172 and miR396, quantification of miRNAs by Northern- blot and target mRNAs by qRT-PCR are being done. Preliminary results show that, as occurs in maize, miR172 decreases 2-fold in UV-B treated plants, while TOE2 and SMZ mRNAs increased around 2-fold and AP2, TOE1, TOE2, and SNZ mRNA levels are not changed by the UV-B treatments. UV-B treated Arabidopsis plants flowered around six days later than under control conditions, correlating with the decrease in miR172 levels, and increased levels of TOE2 and SMZ mRNAs. Also, UV-B treated plants have a smaller size than control plants, which may be due to a decreased GRFs expression measured by qRT-PCR. These results suggest miRNAs could mediate some UV-B responses in maize and Arabidopsis.