The transcription factor BnaA9.WRKY47 coordinates leaf senescence and nitrogen remobilization in Brassica napus.

Abstract

Nitrogen (N) is an essential macronutrient for plants, and N remobilization is key for plant adaptation to N deficiency stress. However, there is a limited understanding of the regulatory mechanisms of N remobilization in Brassica napus. Here, we report a transcription factor, BnaA9.WRKY47, induced by N starvation. At the seedling stage, BnaA9.WRKY47-OE lines displayed earlier senescence of older leaves and preferential growth of juvenile leaves compared to the wild-type 'Westar 10' under N starvation. At the field scale, the seed yield was significantly increased in BnaA9.WRKY47-OE lines compared to 'Westar 10' grown under N deficiency conditions and, conversely, reduced in BnaA9.WRKY47-mutants. Biochemical analyses demonstrate that BnaA9.WRKY47 directly activates BnaC7.SGR1 to accelerate older leaf senescence. In line with leaf senescence, the amino acid concentration was elevated, and the N distribution was reduced in the older leaves of OE lines. This result is because BnaA9.WRKY47 activates the amino acid permease BnaA9.AAP1 and the nitrate transporter BnaA2.NRT1.7. Therefore, the expression of BnaA9.WRKY47 efficiently facilitates N remobilization from older to younger leaves or seeds. Taken together, the results of this study demonstrate that BnaA9.WRKY47 upregulates the expression of BnaC7.SGR1, BnaA2.NRT1.7 and BnaA9AAP1 thus promoting the remobilization of N in B. napus under N starvation.