bHLH92 from sheepgrass acts as a negative regulator of anthocyanin/proanthocyandin accumulation and influences seed dormancy

Sheepgrass (Leymus chinensis) is an important native forage grass, and it is widely grown in north China. Differential dormancy exists in sheepgrass germplasms with different seed colors. To decipher and find potential genes underlying this phenomenon, we compared the transcript profiles of yellow seeds with weak dormancy and brown seeds with strong dormancy. We identified a transcription factor gene LcbHLH92 which is negatively correlated with those of anthocyanin/proanthocyanidin-specific pathway genes, anthocyanidin synthase (ANS) and anthocyanidin reductase (ANR). LcbHLH92 had two transcripts, LcbHLH92a and LcbHLH92b, and their expression could be induced by abscisic acid, cold, and NaCl. Overexpression of LcbHLH92a or LcbHLH92b in Arabidopsis significantly inhibited the transcript levels of dihydroflavonol reductase (DFR) and ANS genes in leaves and seeds, which resulted in a decrease in anthocyanins and proanthocyanidins, respectively. Importantly, transgenic Arabidopsis seeds with a yellow color showed a higher germination rate than did the wild-type with a brown seed color. Moreover, LcbHLH92a and LcbHLH92b repressed the transcription of Transparent Testa8, ANS, DFR, and ANR, possibly by elevating the transcript levels of jasmonate-ZIM domain proteins through binding to their promoters. Together, our results demonstrate that LcbHLH92a and LcbHLH92b are negative regulators of the anthocyanin/proanthocyanidin pathway and influence seed dormancy.