Overexpression of Mir319a Altered Oil Body Morphogenesis and Lipid Content in Arabidopsis Seeds

MicroRNA319a (miR319a) acts as an essential regulator of gene expression during plant development and under stress conditions. Although the role of miR319a in regulating leaf development has been well studied in Arabidopsis, the function of miR319a in regulating seed oil content remains poorly understood. To examine the effects of miR319a on oilseed oil bodies (OBs) and oil content, miR319a was overexpressed in Arabidopsis in this study. Overexpression of 35S:miR319a in transgenic Arabidopsis caused severely crinkled siliques and led to increased total oleosin levels. Electron microscopy revealed that the overexpression of miR319a in transgenic Arabidopsis seeds resulted in more numerous and smaller OBs compared to WT plants, suggesting an inverse relationship between OB size and oleosin levels. Changes in the size of OBs altered the accumulation of lipids and decreased seed lipid contents to 10% in 35S:miR319a-12 and to 6% in 35S:miR319a-85, which were lower than the WT control. The fatty acid profiles indicated that palmitic, linoleic, linolenic, and eicosenoic acids increased by 15.2%, 5.2%, 17.6%, and 26.9%, respectively, on average, compared to WT seeds. Increases in these four fatty acids were compensated by a 24.7% and 38.4% decrease in oleic and erucic acids, respectively. Therefore, these results imply that miR319a is involved in lipid metabolism.