Expression of microRNAs in cotton.

MicroRNAs (miRNAs) are a class of newly identified non-protein-coding small RNAs. miRNAs post-transcriptionally regulate the expression of more than 30% genes, which control many biological and metabolic progresses, including plant growth, development, and response to environmental stresses. However, no studies have been performed on miRNA expression in cotton, one of the most important fiber and economic crops. In this study, we employed quantitative real-time PCR (qRT-PCR) to detect and compare miRNA expressions in eight different cotton organs at different developmental stages. Our results showed that miRNAs were differentially expressed in different cotton organs, with certain classes expressed preferentially in an organ-specific manner. The miR-156 was highly expressed in cotyledon, whereas the miR-172 was highly expressed in young leaves at fruit branch, young flower buds, 0 day post-anthesis (DPA) ovules, and 0 DPA petals. We also found that miR-172 was not highly expressed in all parts of flowers. In contrast, miR-172 was highly expressed in petal but not in stamen and carpel. Interestingly, miR-162 was highly expressed in immature fiber, 2 DPA ovules, and mixtures of 0 DPA stamen and carpel, suggesting miR-162 may play a role in cotton fiber differentiation and development. Our previous study showed that miR-396 may target a fiber-related gene the callose synthase catalytic subunit. In this study, the miR-396 expression was observed in all eight cotton organs. This study identified the expression of miRNAs that may regulate the development of cotton and cotton fiber.