Identification of tissue-preferential expression patterns of rice miRNAs.

It is imperative to understand the mechanisms of growth and development in higher plants for improving plant adaptation during different developmental stages. Plant microRNAs (miRs) play crucial regulatory roles in various developmental processes. As many as 15 miR families having multiple members are known to regulate plant development, yet the spatio-temporal expression patterns of individual members are not fully characterized. It is likely that different members of miR families can make specific contributions to the spatio-temporal control of targets. To understand the functional complexity of miRs and the amount of degeneracy existing in miR-mediated regulation of differentiated but developing tissues, we have identified the Osa-miR-sequences that are expressed in specific tissues. We adopted the approach of comparative miR profiling using next-generation sequencing technology followed by experimental validation. It was observed that 59 Osa-miR-sequences show tissue-preferential expression in local basmati rice variety; while 126 miRs belonging to 81 families are differentially regulated in these tissues. The 21 nt miRs were predominant in all tissues, but the 24 nt miRs were the most abundantly expressed. This indicates that target cleavage and chromatin state regulation are involved in organ development. This study also identified the expression patterns of individual members of Osa-miR families that were common and divergent between the indica and japonica rice varieties. The expression patterns of the predicted targets were also analyzed. The possible implications of the miR distribution patterns with respect to the regulation of their respective targets are discussed.