Abstract
BackgroundRice is a major crop feeding the majority of the global population, and increasing its sink strength is one of the modes to alleviate the declining availability of food for the rapidly growing world population. We demonstrate a role for an important rice vacuolar invertase isoform, OsINV3, in sink strength determination.ResultsOsINV3 mutants showed shorter panicles with lighter and smaller grains, owing to a smaller cell size on the outer and inner surfaces of the palea and lemma as observed by scanning electron microscopy. Further, strong promoter::GUS expression was observed in the palea, lemma and the rachis branches in the young elongating panicles, which supported the role of OsINV3 in cell expansion and thus, in spikelet size and panicle length determination. Size of the spikelet was found to directly influence the grain weight, which was confirmed by the lack of differences in weights of hulled grain for differently segregated alleles in the heterozygous lines. Assessment of field grown mutants not only revealed a drastic reduction in the percentage of ripened grain, 1000-grain weight and final yield, but also significantly reduced partitioning of assimilates to the panicles, whereby the total dry weight remained unaffected. Determination of the non-structural carbohydrate contents revealed a lower hexose-to-sucrose ratio in the panicles of the mutants from panicle initiation to 10 days after heading, a stage that identifies as the critical pre-storage phase of grain filling, whereas the starch contents were not affected. In addition, strong promoter::GUS expression was observed in the dorsal end of ovary during the pre-storage phase until 6 days after flowering, highlighting a function for OsINV3 in monitoring the initial grain filling stage.ConclusionsOsINV3 was found to regulate spikelet size by playing a key role in cell expansion, driving the movement of assimilates for grain filling by modulating the hexose-to-sucrose ratio, contributing in grain weight determination and thus, the grain yield.
Highlights
Rice is a major crop feeding the majority of the global population, and increasing its sink strength is one of the modes to alleviate the declining availability of food for the rapidly growing world population
The present study examines the physiological role of a Vacuolar invertase (VIN) isogene, OsINV3, in rice, in terms of sink size and assimilate partitioning, in concert with analysis of cell size and sink sugar composition, establishing evidence for its role as a molecular sink strength determinant
Genotyping of the Wild type (WT), mutant and the complementation lines C3, C4 and C13 confirmed a homozygous insertion of the Tos17 retrotransposon in the second exon of the OsINV3 gene in the mutants, and subsequent successful incorporation of OsINV3 gene in the mutant lines, enabling an effective complementation (Fig. 1c)
Summary
Rice is a major crop feeding the majority of the global population, and increasing its sink strength is one of the modes to alleviate the declining availability of food for the rapidly growing world population. A major photoassimilate in plants, plays an important role in carbon allocation, by osmotically controlling the flux, and by generating hexose-based signals to regulate genes involved in carbon metabolism in the sink organs (Herbers and Sonnewald 1998; Smeekens 2000; Koch 2004). The enzymes that catalyze sucrose cleavage are considered to be potential molecular contributors to sink strength (Herbers and Sonnewald 1998). One such class of enzymes are the invertases (EC 3.2.1.26) that catalyze the irreversible cleavage of sucrose into glucose and fructose. The entry of sucrose into different utilization pathways is regulated by various isoforms of invertases (Sturm 1999)
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