A Conserved miR394-Targeted F-Box Gene Positively Regulates Drought Resistance in Foxtail Millet

One of the oldest crops, foxtail millet (Setaria italica), is regarded as a model plant for studying drought tolerance owing to its short life-cycle and small genome size. The miRNA member miR394 plays multifaceted roles in plants. In this study, we identified the Sit-miR394 target gene SiFBP6 using 5′ RLM-RACE (RNA ligase mediated rapid amplification of 5′ cDNA ends). An expression analysis in different tissues showed that Sit-miR394 was highly expressed in leaves and had a lower relative expression in roots, while the target gene SiFBP6 exhibited the opposite expression pattern, being strongly expressed in roots and relatively lowly expressed in leaves. Furthermore, Sit-miR394 was upregulated in foxtail millet under drought-stress conditions and by exogenous methyl jasmonate, ethephon, salicylic acid and abscisic acid treatments. The overexpression of Sit-miR394 in transgenic Arabidopsis thaliana increased its tolerance to drought stress. The germination rates and root lengths were significantly greater compared with the wild-type line, which suggested that Sit-miR394 plays a positive role in responding to drought conditions. Moreover, a transcription analysis indicated that the overexpression of Sit-miR394 affected the expression of a set of stress-related genes, thereby conferring an increased abiotic or biotic stress tolerance to transgenic Arabidopsis. Thus, Sit-miR394 functions in the positive modulation of abiotic or biotic stress tolerance and has potential applications in molecular breeding to enhance stress tolerance in crops.