Proteomic profiling reveals differentially expressed proteins associated with amylose accumulation during rice grain filling.

BACKGROUND: Amylose accumulation in rice grains is controlled by genetic and environmental factors. Amylose content is a determinant factor of rice quality in terms of cooking and eating. Great variations in amylose content in indica rice cultivars have been observed. The current study was to identify differentially expressed proteins in starch and sucrose metabolism and glycolysis/gluconeogenesis pathways and their relationships to amylose synthesis using two rice cultivars possess contrasting phenotypes in grain amylose content. RESULTS: Synthesis and accumulation of amylose in rice grains significantly affected the variations between rice cultivars in amylose contents. The high amylose content cultivar has three down-regulated differentially expressed proteins, i.e., LOC_Os01g62420.1, LOC_Os02g36600.1, and LOC_Os08g37380.2 in the glycolysis/gluconeogenesis pathway, which limit the glycolytic process and decrease the glucose-1-phosphate consumption. In the starch and sucrose metabolic pathway, an up-regulated protein, i.e., LOC_Os06g04200.1 and two down-regulated proteins, i.e., LOC_Os05g32710.1 and LOC_Os04g43360.1 were identified (Figure 4). Glucose-1-phosphate is one of the first substrates in starch synthesis and glycolysis that are catalyzed to form adenosine diphosphate glucose (ADPG), then the ADPG is catalyzed by granule-bound starch synthase I (GBSS I) to elongate amylose. CONCLUSIONS: The results indicate that decreasing the consumption of glucose-1-phosphate in the glycolytic process is essential for the formation of ADPG and UDPG, which are substrates for amylose synthesis. In theory, amylose content in rice can be regulated by controlling the fate of glucose-1-phosphate.

The nicotine demethylase CYP82E4 is essential for the formation of red dapples on flue-cured leaves of cherry-red tobacco.

Common flue-cured tobacco (Nicotiana tabacum L.) primarily accumulates nicotine, and its flue-cured leaves exhibit a lemon appearance. In contrast, a spontaneous cherry-red variant (CR60) primarily accumulates nornicotine, accompanied by distinctive red dapples on the cured leaves. In this study, suppression of conversion of nicotine to nornicotine by genome editing resulted in decreased nornicotine and N-acyl nornicotines (NacNNs), and the subsequent disappearance of red dapples in CR60. Conversely, overexpression of CYP82E4 increased nornicotine and NacNNs accumulation, inducing a red dapple phenotype in common tobacco. Notably, nicotine conversion triggered significant alterations in leaf total sugars, alkaloids, and nitrogens. Metabolome analyses using 1352 identified compounds indicated nicotine conversion dramatically affected the entire metabolic network and induced unique metabolic responses across diverse genetic backgrounds. Further WGCNA analysis revealed that nicotine conversion caused substantial contents variation of alkaloids, flavonoids and amino acids and derivatives in cured leaves. Overall, this research provides valuable insights into the mechanisms underlying red dapple formation in cherry-red tobacco, elucidating profound influence of nicotine conversion on entire metabolic network.

Primary-tiller panicle number is critical to achieving high grain yields in machine-transplanted hybrid rice.

The development of machine-transplanted hybrid rice is a feasible approach to meet the needs of both high grain yield and high labor efficiency in China, but limited information is available on the critical plant traits associated with high grain yields in machine-transplanted hybrid rice. This study was carried out to identify which type of culms (i.e., main stems and primary and secondary tillers) and which yield components of this culm are critical to achieving high grain yields in machine-transplanted hybrid rice. Field experiments were conducted with two hybrid rice cultivars grown under two densities of machine transplanting in two years. Results showed that total grain yield of main stems and primary and secondary tillers was not significantly affected by cultivar but was significantly affected by density and year. Averaged across cultivars, densities, and years, main stems and primary and secondary tillers contributed about 15%, 50%, and 35% to total grain yield, respectively. Total grain yield was not significantly related to grain yields of main stems and secondary tillers but was positively and significantly related to grain yield of primary tillers. Approximately 85% of the variation in total grain yield was explained by grain yield of primary tillers, which was positively and significantly related to primary-tiller panicles per m2 but not to spikelets per panicle, spikelet filling percentage, or grain weight of primary tillers. Based on these results, it is concluded that primary-tiller panicle number is essential for achieving high grain yields in machine-transplanted hybrid rice.

Genotypic variation in the grain photosynthetic contribution to grain filling in rice.

Grain filling in rice, a staple cereal crop worldwide, is a critical determinant of grain yield and quality. However, there is little available information on the relationship between grain filling and grain photosynthetic capacity in rice. This study evaluated the genetic diversity among six rice cultivars for their grain filling rate (GR0) and the relationships with the grain chlorophyll contents and grain net photosynthetic rate (PN). Significant variations in GR0, PN, and the chlorophyll contents (a, b, and total) in the grains of the cultivars were observed. Approximately 90 % of the variation in GR0 was explained by the grain PN. General linear model regression revealed significant positive correlations between PN/GR0 and the chlorophyll contents (a, b, and total) in the grains. There was also a significant positive correlation between PN and GR0. These positive correlations suggest a direct positive relationship between the grain filling rate and grain chlorophyll contents, which is indicative of the high photosynthetic capacity of the grains during the early grain filling period. These results suggest that the grain chlorophyll contents could be used as a molecular marker in marker-assisted breeding programs for rice cultivars with high grain net photosynthetic capacity during the early period of grain filling to improve grain yield.

Grain filling of early-season rice cultivars grown under mechanical transplanting.

High yields of mechanized intensive rice-based cropping systems, e.g. double-season cropping using early- and late-season rice, are important to ensure national food security in China. However, few studies addressing the relationship between grain weight and grain yield of early-season rice under machine-transplanted conditions. A field experiment was conducted to determine the critical grain-filling characteristics and related physiological aspects that contribute to high grain weight in machine-transplanted early-season rice. The results showed that grain yield was significantly positively correlated with grain weight but not with panicles per m2, spikelets per panicle, and spikelet-filling percentage. Furthermore, this study demonstrated that there was a significant positive correlation between grain weight and mean grain-filling rate, which was significantly positively correlated with harvest index and grain cytokinin content. These results indicate that high grain-filling rate driven by good transport of assimilates to grains and strong grain sink strength is responsible for high grain weight in machine-transplanted early-season rice.

Higher yields of hybrid rice do not depend on nitrogen fertilization under moderate to high soil fertility conditions.

BACKGROUND: Increasing rice yield with fewer external inputs is critical to ensuring food security, reducing environmental costs, and improving returns. Use of hybrid rice has expanded greatly in China due to its higher yield potential. Meanwhile, large and increasing amounts of nitrogen (N) fertilizers have been used for expanding rice production in China. It is not clear to what extent the success of hybrid rice in China is associated with N fertilizer inputs. FINDINGS: We observed that the higher grain yield with N fertilizer in hybrid rice was driven more by a higher yield without N fertilizer than by increases in grain yield with N fertilizer under moderate to high soil fertility conditions. CONCLUSIONS: Our results suggest that greater application of N fertilizers is not needed to benefit from hybrid rice production under moderate to high soil fertility conditions, and that improving and maintaining soil fertility should be a focus for sustaining hybrid rice production. Moreover, our study also indicates that zero-N testing may be a potentially useful tool to develop hybrid rice with high yield and without requirement of greater external N inputs under moderate to high soil fertility conditions.