Roles of the Brassica napus DELLA Protein BnaA6.RGA, in Modulating Drought Tolerance by Interacting With the ABA Signaling Component BnaA10.ABF2

Drought is a major threat to plant growth and crop productivity. Reduced level of the gibberellin would result in increased drought tolerance, but the underlying mechanism is still unclear. In <i>Brassica napus</i>, there are four <i>BnaRGA</i> genes that code for DELLA proteins, negative regulators of GA signaling. Among them, expression of <i>BnaA6.RGA</i> was greatly induced by drought and abscisic acid (ABA). Previously, we created the gain-of-function mutant of <i>BnaA6.RGA</i>, <i>bnaa6.rga-D</i>, and the loss-of-function quadruple mutant, <i>bnarga</i> by CRISPR/Cas9, respectively. Here we show that <i>bnaa6.rga-D</i> displayed enhanced drought tolerance, and its stomatal closure was hypersensitive to ABA treatment. By contrast, <i>bnarga</i> displayed reduced drought tolerance and was less sensitive to ABA treatment, but there is no difference in drought tolerance between single <i>BnaRGA</i> mutant and WT, suggesting a functional redundancy between the <i>BnaRGA</i> genes in this process. Furthermore, we found that BnaRGAs were able to interact physically with BnaA10.ABF2, an essential transcription factor in ABA signaling. The BnaA10.ABF2-BnaA6.RGA protein complex greatly increased the expression level of the drought responsive gene <i>BnaC9.RAB18</i>. Taken together, this work highlighted the fundamental roles of DELLA proteins in drought tolerance in <i>B. napus</i>, and provide desirable germplasm for further breeding of drought tolerance in rapeseed.