The effect of BnTT8 on accumulation of seed storage reserves and tolerance to abiotic stresses during Arabidopsis seedling establishment

Previous studies have revealed that a basic helix–loop–helix domain transcription factor AtTT8 is not only involved in biosynthesis of anthocyanins and proanthocyanidins, but also regulates seed development and oil biosynthesis in Arabidopsis. However, the functions of BnTT8 in accumulation of seed storage reserves and seedling establishment remain largely unclear. Here, we obtained the BnTT8 coding domain sequence from the Brassica napus cultivar QINYOU Seven, and analyzed its conserved protein domains. A subcellular localization experiment in tobacco leaves indicated that BnTT8 functioned as a transcription factor. Expression analysis indicated that TT8 was widely expressed in various tissues, and was also predominantly present in developing seeds of QINYOU Seven. Our results strongly demonstrated that introduction of BnTT8 into the tt8-4 mutant could fully complement many phenotypes of tt8-4 seeds, such as yellow seed coat, higher fatty acid content, and lower storage protein content. We also found that ectopic expression of BnTT8 successfully corrected the sensitivity of the tt8-4 mutant to salinity and glucose stresses during seed germination and seedling establishment. Moreover, altered expression levels of many stress-responsive genes in tt8-4 seedlings were rescued to wild-type levels by ectopic expression of BnTT8 . These results should improve understanding of the entire function of BnTT8 and provide promising targets for genetic manipulations of B. napus to improve oil quantity in seeds.