Virus-Induced Gene Silencing Identifies an Important Role of the TaRSR1 Transcription Factor in Starch Synthesis in Bread Wheat

The function of a wheat starch regulator 1 (TaRSR1) in regulating the synthesis of grain storage starch was determined using the barley stripe mosaic virus-virus induced gene-silencing (BSMV-VIGS) method in field experiments. Chlorotic stripes appeared on the wheat spikes infected with barley stripe mosaic virus-virus induced gene-silencing-wheat starch regulator 1 (BSMV-VIGS-TaRSR1) at 15 days after anthesis, at which time the transcription levels of the TaRSR1 gene significantly decreased. Quantitative real-time PCR was also used to measure the transcription levels of 26 starch synthesis-related enzyme genes in the grains of BSMV-VIGS-TaRSR1-silenced wheat plants at 20, 27, and 31 days after anthesis. The results showed that the transcription levels of some starch synthesis-related enzyme genes were markedly induced at different sampling time points: TaSSI, TaSSIV, TaBEIII, TaISA1, TaISA3, TaPHOL, and TaDPE1 genes were induced at each of the three sampling time points and TaAGPS1-b, TaAGPL1, TaAGPL2, TaSSIIb, TaSSIIc, TaSSIIIb, TaBEI, TaBEIIa, TaBEIIb, TaISA2, TaPHOH, and TaDPE2 genes were induced at one sampling time point. Moreover, both the grain starch contents, one thousand kernel weights, grain length and width of BSMV-VIGS-TaRSR1-infected wheat plants significantly increased. These results suggest that TaRSR1 acts as a negative regulator and plays an important role in starch synthesis in wheat grains by temporally regulating the expression of specific starch synthesis-related enzyme genes.