The sunflower transcription factor HaHB11 improves yield, biomass and flood tolerance via the quiescent response in transgenic plants

HaHB11 is a divergent member of the sunflower homeodomain-leucine zipper I subfamily of transcription factors. A sunflower microarray was hybridized with RNA from HaHB11-transformed leaf-disks and its analysis indicated the regulation of many genes encoding enzymes from fermentative pathways. A 1300 bp sequence exhibiting flooding-responsive cis-acting elements, upstream the transcription initiation site, was isolated and Arabidopsis plants transformed with a construct in which this promoter directs GUS expression. GUS expression was induced after flooding treatments and, in the same sense, HaHB11 expression was induced by flooding stress in sunflower. Furthermore, Arabidopsis plants were transformed with different constructs, varying in the promoter used, able to express HaHB11 cDNA. These transgenic plants exhibited differential phenotypes which the more remarkable traits were a significant increase in the rosette biomass and seeds yield. Moreover these plants exhibited an enhanced tolerance to flooding stress, both to submergence and waterlogging. Starch, sucrose and glucose contents were higher in the transgenics compared to WT and decreased less after submergence treatments. Finally, transcript levels of selected genes, involved in fermentative pathways, and the corresponding enzymatic activities were assessed both in sunflower and transgenic Arabidopsis plants after submergence indicating a general repression of the fermentative pathway which suggested that tolerance occurs via the quiescent strategy. Altogether the results indicated a role for HaHB11 in the flooding response and allowed us to propose this gene as a biotechnological tool to improve crops for increased yield and biomass and flooding tolerance. Transient sunflower discs (Manavella and Chan, Nature Protocols 2009) 35S Promoter::GUS vs. 35S Promoter::HaHB11. Three biological replicates each.