Abstract
High temperature stress during rice reproductive development results in yield losses. Reduced grain yield and grain quality has been associated with high temperature stress, and specifically with high night-time temperatures (HNT). Characterizing the impact of HNT on the phenotypic and metabolic status of developing rice seeds can provide insights into the mechanisms involved in yield and quality decline. Here, we examined the impact of warmer nights on the morphology and metabolome during early seed development in six diverse rice accessions. Seed size was sensitive to HNT in four of the six genotypes, while seed fertility and seed weight were unaffected. We observed genotypic differences for negative impact of HNT on grain quality. This was evident from the chalky grain appearance due to impaired packaging of starch granules. Metabolite profiles during early seed development (3 and 4 days after fertilization; DAF) were distinct from the early grain filling stages (7 and 10 DAF) under optimal conditions. We observed that accumulation of sugars (sucrose, fructose, and glucose) peaked at 7 DAF suggesting a major flux of carbon into glycolysis, tricarboxylic acid cycle, and starch biosynthesis during grain filling. Next, we determined hyper (HNT > control) and hypo (HNT < control) abundant metabolites and found 19 of the 57 metabolites to differ significantly between HNT and control treatments. The most prominent changes were exhibited by differential abundance of sugar and sugar alcohols under HNT, which could be linked to a protective mechanism against the HNT damage. Overall, our results indicate that combining metabolic profiles of developing grains with yield and quality parameters under high night temperature stress could provide insight for exploration of natural variation for HNT tolerance in the rice germplasm.
Highlights
Rice (Oryza sativa) is a staple food crop for over half the world’s population, especially in Asia where 90% of rice is produced and consumed and provides 50% of the dietary caloric supply (Khush, 2005; Khush and Jena, 2009; Muthayya et al, 2014)
Rice response to high night-time temperatures (HNT) at metabolic levels have been reported for leaves, where accumulation of amino acids, organic acids, sugars, polyols, and putrescine, as well as mis-regulation of the TCA cycle was observed (Glaubitz et al, 2015; Glaubitz et al, 2017). These results indicate the influence of sugar metabolism on the rice yield under HNT, the effect of HNT on metabolite profiles of developing seeds remain less explored
Our results indicated alteration in mature seed size and structural impairment of starch granules due to HNT, whereas no differences were observed with respect to percentage fertility and seed weight
Summary
Rice (Oryza sativa) is a staple food crop for over half the world’s population, especially in Asia where 90% of rice is produced and consumed and provides 50% of the dietary caloric supply (Khush, 2005; Khush and Jena, 2009; Muthayya et al, 2014). HTS during grain filling impacts the final grain weight and leads to structural abnormalities in starch granules, which causes an overall increase in chalkiness, lowering the rice quality for human consumption (Lisle et al, 2000; Fitzgerald and Resurreccion, 2009; Ishimaru et al, 2009; Tsutsui et al, 2013) These abnormalities have been linked to insufficient supply of nutrients to the developing endosperm, reduction in starch synthesis or premature degradation of starch (Sato and Inaba, 1976; Yamakawa et al, 2007; Ishimaru et al, 2009)
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