Abstract
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.
Highlights
Starch is the major storage carbohydrate reserve in the endosperm of cereals, including rice, wheat, and maize, and provides about 80% of the calories consumed by humans [1]
Fu and Xue [22] reported that the transcription levels of OsRSR1 were almost opposite those of 15 rice starch synthesis-related enzyme genes (OsAGPS1, OsAGPS2, OsAGPL1, OsAGPL2, OsGBSSI, OsSSI, OsSSIIa, OsSSIIIa, OsBEI, OsBEIIb, OsISA1, OsISA2, OsISA3, OsPHOL, and OsPUL), and in an rsr1 mutant, these genes were distinctly upregulated during the early stage (6 days) of the grain-filling period when grain starch contents significantly increased
Our previous data indicated that the transcription levels of TaRSR1 were significantly negatively correlated with those of 11 starch synthesis-related enzyme genes (TaAGPS1-a, TaAGPL1, TaGBSSI, TaSSI, TaSSIIa, TaSSIV, TaBEI, TaBEIIb, TaPUL, TaPHOL, and TaDPE1) during the entire grain-filling period (35 days) of bread wheat, suggesting that TaRSR1 negatively regulates the expression of these genes and affects grain starch synthesis
Summary
Starch is the major storage carbohydrate reserve in the endosperm of cereals, including rice, wheat, and maize, and provides about 80% of the calories consumed by humans [1]. Plant starch is composed of two different glucose polymers: amylose and amylopectin. The former is a linear polymer composed of α-1,4-glucosidic chains, whereas the latter consists of a highly branched glucan with α-1,6 glucosidic bonds that connect linear chains [2]. Amylose is synthesized by adenosine diphosphate glucose pyrophosphorylase (AGPase, EC 2.7.7.27) and granule-bound starch synthase (GBSS, EC 2.4.1.21), whereas amylopectin is catalyzed by the coordinated actions of AGPase, soluble starch synthase AGPase catalyzes adenosine diphosphate glucose (ADP-Glc) to glucose-1-phosphate (G-1-P) and provides substrates for amylose and amylopectin synthesis. GBSS is a key enzyme involved in amylose synthesis, whereas SS, BE, and DBE function together with distinct roles to catalyze amylopectin synthesis [2,3]. PHO and DPE are believed to be involved in the initiation steps, elongating α-1,4-linked glucan polymers using G-1-P as substrate, their precise mechanisms remain unclear [2,4]
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