Starch reduction in rice stems due to a lack of OsAGPL1 or OsAPL3 decreases grain yield under low irradiance during ripening and modifies plant architecture

Abstract

Starch accumulated in rice (Oryza sativa L.) stems before heading as nonstructural carbohydrates (NSCs) is reported to be important for improving and stabilising grain yield. To evaluate the importance of stem starch, we investigated a retrotransposon (Tos17) insertion rice mutant lacking a gene encoding a large subunit of ADP-glucose pyrophosphorylase (AGP) called OsAGPL1 or OsAPL3. The AGP activity and starch contents of the mutant were drastically reduced in the stem (i.e. leaf sheath and culm) but not in the leaf blade or endosperm. This starch reduction in the leaf sheaths of the mutant was complemented by the introduction of wild-type OsAGPL1. These results strongly suggest that OsAGPL1 plays a principal role in stem starch accumulation. Field experimentations spanning 2 years revealed that the mutant plants were shorter than the wild-type plants. Moreover, the tiller number and angle were larger in the mutant plants than the wild-type plants, but the dry weight at heading stage was not different. The grain yield was slightly lower in control plots without shading treatment. However, this difference increased substantially with shading. Therefore, stem starch is indispensable for normal ripening under low irradiance conditions and probably contributes to the maintenance of appropriate plant architecture.

Phenotypic plasticity conditions the response of soybean seed yield to elevated atmospheric CO2 concentration

“…After the measurements, the portions of four leaves from four plants were excised, frozen in N 2 , and then dried at 80°C for 3 d in the oven for determination of NSC content (starch and soluble sugar content). NSCs were extracted and measured as described previously (Okamura et al, 2013). Soluble sugar content was defined as the sum of Suc, Glc, and Fru contents.…”

Characterization of sugar metabolism in the stem of Tachisuzuka, a whole-crop silage rice cultivar with high sugar content in the stem

“…Similarly, the enzyme activities of AGP, a key enzyme in starch synthesis (Okamura et al, 2013(Okamura et al, , 2015, in the leaf sheath and internodes of TS were significantly higher than those in KH but not significantly different from those in KH-PR ( Figure 4(K) and (L)). These results suggest that the differences in starch content in the stem are mainly due to the amount of carbon translocated to the stems, which is affected by panicle size.…”

“…AGP catalyzes the conversion of glucose 1-phosphate to ADP-glucose and is a key enzyme in starch synthesis in rice stem (Okamura et al, 2013(Okamura et al, , 2015. AGP activities in the leaf sheaths and internodes of TS were significantly higher and fructose (Strum & Tang, 1999).…”

“…Total RNA was extracted from LS3 of TS and KH as described previously by Okamura et al (2013). The RNA samples from at least four different plants were collected for each variety and analyzed as one sample.…”

“…AGP, SPS, and SUS activities were evaluated as described previously by Okamura et al (2013), Hashida et al (2016), and Hirose et al (2008), respectively. CWIN, NIN, and VIN were evaluated as described previously by Ishimaru et al (2005) with some modifications.…”