MicroRNAs in cotton: an open world needs more exploration

Qinglian Wang, Baohong Zhang

This paper reviews the progress and current problems in the field of cotton microRNAs. Cotton is not only one of the most important crops in terms of fiber usage and economic value, but also a model species for investigating cell wall and cellulose biosynthesis as well plant polyploidization. Compared with model plant species, such as Arabidopsis and rice, the research on cotton microRNAs (miRNAs) is lagging, although great progress has been made in the past decade. Since the first reports on identifying miRNAs in cotton in 2007, hundreds of miRNAs have been identified using an in silico comparative genome-based approach and direct cloning. Next-generation deep sequencing has opened the door for cotton miRNA research. In cotton, miRNAs are associated with many biological and metabolic processes, including fiber initiation and development, floral development, embryogenesis, and response to biotic and abiotic stresses. However, the majority of current research is focused on miRNA identification. Although several targets have been predicted using computational approaches and degradome sequencing, more functional studies should be performed in the next couple of years to elucidate the roles of miRNAs in cotton fiber development and response to different environmental stresses using transgenic technology. This paper reviews the history, identification, and function of cotton miRNAs as well as future directions for this research.