A sunflower WRKY transcription factor stimulates the mobilization of seed-stored reserves during germination and post-germination growth

Germinating oilseeds convert stored lipids into sugars and thereafter in metabolic energy that is used in seedling growth and establishment. During germination, the induced lipolysis linked to the glyoxylate pathway and gluconeogenesis produces sucrose, which is then transported to the embryo and driven through catabolic routes. Herein, we report that the sunflower transcription factor HaWRKY10 regulates carbon partitioning by reducing carbohydrate catabolism and increasing lipolysis and gluconeogenesis. HaWRKY10 was regulated by abscisic acid and gibberellins in the embryo leaves and highly expressed during sunflower seed germination and seedling growth, concomitantly with lipid mobilization. Sunflower leaf discs overexpressing HaWRKY10 showed repressed the expression of genes related to sucrose cleavage and glycolysis compared to controls. Moreover, HaWRKY10 constitutive expression in Arabidopsis seeds produced higher decrease in lipid reserves, whereas starch and sucrose were more preserved compared to wild type. Gene transcripts abundance and enzyme activities involved in stored lipid mobilization and gluconeogenesis increased more in transgenic than in wild type seeds 36 hours after imbibition whereas the negative regulator of lipid mobilization, ABI4, was repressed. Altogether, the results point out a functional parallelism between tissues and plant species, and reveal HaWRKY10 as a positive regulator of storage reserve mobilization in sunflower. Transient sunflower discs (Manavella and Chan, Nature Protocols 2009) 35S Promoter::GUS vs. 35S Promoter::HaHB11. Three biological replicates each.