Abstract
Cultivars of rice (Oryza sativa L.), especially of the type with large spikelets, often fail to reach the yield potential as expected due to the poor grain-filling on the later flowering inferior spikelets (in contrast to the earlier-flowering superior spikelets). The present study showed that the size and grain weight of superior spikelets (SS) was greater than those of inferior spikelets (IS), and the carbohydrate supply should not be the major problem for the poor grain-filling because there was adequate amount of sucrose in IS at the initial grain-filling stage. High resolution two-dimensional gel electrophoresis (2-DE) in combination with Coomassie-brilliant blue (CBB) and Pro-Q Diamond phosphoprotein fluorescence stain revealed that 123 proteins in abundance and 43 phosphoproteins generated from phosphorylation were significantly different between SS and IS. These proteins and phosphoproteins were involved in different cellular and metabolic processes with a prominently functional skew toward metabolism and protein synthesis/destination. Expression analyses of the proteins and phosphoproteins associated with different functional categories/subcategories indicated that the starch synthesis, central carbon metabolism, N metabolism and cell growth/division were closely related to the poor grain-filling of IS. Functional and expression pattern studies also suggested that 14-3-3 proteins played important roles in IS poor grain-filling by regulating the activity of starch synthesis enzymes. The proteome and phosphoproteome obtained from this study provided a better understanding of the molecular mechanism of the IS poor grain-filling. They were also expected to be highly useful for improving the grain filling of rice.
Highlights
Rice (Oryza sativa L.) is one of the world’s most important staple crops
It is commonly believed that the poor inferior spikelets (IS) grain-filling was due to a limited carbohydrate supply [22,23]
The present study showed that the soluble carbohydrates in grains on IS was higher than SS during EGS and mid-grain-filling stages (MGS), indicating that the carbohydrate supply should be more abundant in IS than SS
Summary
Rice (Oryza sativa L.) is one of the world’s most important staple crops. It is essential for global food security, especially in the populous Asian and African regions [1]. The grains of rice grow on the spikelets, which can be classified as SS or IS according to their location on a branch and the time of flowering [2,3]. The poor grain-filling of IS on rice cultivars, especially for the ‘‘super’’ varieties developed recently that bear numerous spikelets per panicle, has become a subject for study, as it negatively affects the final yield and the milling and quality of the rice [5,6,7]
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