The miR166d/TaCPK7-D Signaling Module Is a Critical Mediator of Wheat (Triticum aestivum L.) Tolerance to K(+) Deficiency

It is well established that potassium (K(+)) is an essential nutrient for wheat (Triticum aestivum L.) growth and development. Several microRNAs (miRNAs), including miR166, are reportedly vital roles related to plant growth and stress responses. In this study, a K(+) starvation-responsive miRNA (miR166d) was identified, which showed increased expression in the roots of wheat seedlings exposed to low-K(+) stress. The overexpression of miR166d considerably increased the tolerance of transgenic Arabidopsis plants to K(+) deprivation treatment. Furthermore, disrupting miR166d expression via virus-induced gene silencing (VIGS) adversely affected wheat adaptation to low-K(+) stress. Additionally, miR166d directly targeted the calcium-dependent protein kinase 7-D gene (TaCPK7-D) in wheat. The TaCPK7-D gene expression was decreased in wheat seedling roots following K(+) starvation treatment. Silencing TaCPK7-D in wheat increased K(+) uptake under K(+) starvation. Moreover, we observed that the miR166d/TaCPK7-D module could affect wheat tolerance to K(+) starvation stress by regulating TaAKT1 and TaHAK1 expression. Taken together, our results indicate that miR166d is vital for K(+) uptake and K(+) starvation tolerance of wheat via regulation of TaCPK7-D.