Regulation of cell proliferation by microRNA families in Arabidopsis thaliana.

RAMIRO ESTEBAN RODRIGUEZ; HEIKE WOLLMANN; MARTIN MECCHIA; CARLA SCHOMMER; NICOLAS BOLOGNA; JERÔME BOISBOUVIER; DETLEF WEIGEL; JAVIER PALATNIK

Sydney

Congreso; 7th Human Frontier Science Program Awardees Meeting; 2007

MicroRNAs are small RNAs of 20-21 nt that regulate gene expression in animals and plants. They recognize target sequences in other longer RNAs and guide them to degradation or translational arrest. In general, animal microRNAs recognize multiple target sites with low complementarity that are located in the 3’UTR of target mRNAs and inhibit their translation. Plant microRNAs have usually better complementarity to their targets than their animal counterparts and in most cases recognize only one target sequence located within the coding sequence of the target mRNAs and guide them to degradation. Most of the genes regulated by conserved microRNAs in plants are involved in the regulation of transcription and hormone signaling. We have previously identified 5 TCP transcription factors as targets of miR319a using an experimental approach. These transcription factors inhibit cell proliferation and are required to maintain the flat structure of the leaf. Overexpression of miR319a causes the degradation of TCP transcription factors, excess of cell proliferation and changes in leaves morphogenesis which become crinkly. Target predictions for miR319a include also several MYB transcription factors that are required for stamen development. Interestingly, these MYBs are also targeted by another microRNA miR159. We have developed a method to differentiate between MYB-targeting by miR319 and miR159 in vivo. Our experimental results have shown that miR319 can target both TCPs and MYBs in plants, but the low abundance of this miRNA compared to miR159, causes that the regulation of the MYBs by miR319a play at most a minor role in vivo. The abundant miR159 is therefore involved in MYB regulation, while miR319 is involved in the control of the TCPs and cell proliferation. We have characterized the effects of other miRNA systems from Arabidopsis thaliana on the leaf morphogenesis. Modification of their level can alter the number and size of the cells in the leaf, but the final shape of the organ can be affected in different ways or not modified at all. The results suggest that several miRNAs are involved in the control leaf development but they may be acting at different hierarchical levels.