Comprehensive Expression Profiling of Rice Grain Filling-Related Genes under High Temperature Using DNA Microarray

Abstract

To elucidate the effect of high temperature on grain-filling metabolism, developing rice (Oryza sativa) 'Nipponbare' caryopses were exposed to high temperature (33°C/28°C) or control temperature (25°C/20°C) during the milky stage. Comprehensive gene screening by a 22-K DNA microarray and differential hybridization, followed by expression analysis by semiquantitative reverse transcription-PCR, revealed that several starch synthesis-related genes, such as granule-bound starch synthase I (GBSSI) and branching enzymes, especially BEIIb, and a cytosolic pyruvate orthophosphate dikinase gene were downregulated by high temperature, whereas those for starch-consuming a-amylases and heat shock proteins were up-regulated. Biochemical analyses of starch showed that the high temperature-ripened grains contained decreased levels of amylose and long chain-enriched amylopectin, which might be attributed to the repressed expression of GBSSI and BEIIb, respectively. SDS-PAGE and immunoblot analysis of storage proteins revealed decreased accumulation of 13-kD prolamin, which is consistent with the diminished expression of prolamin genes under elevated temperature. Ripening under high temperature resulted in the occurrence of grains with various degrees of chalky appearance and decreased weight. Among them, severely chalky grains contained amylopectin enriched particularly with long chains compared to slightly chalky grains, suggesting that such alterations of amylopectin structure might be involved in grain chalkiness. However, among high temperature-tolerant and sensitive cultivars, alterations of neither amylopectin chain-length distribution nor amylose content were correlated to the degree of grain chalkiness, but rather seemed to be correlated to grain weight decrease, implying different underlying mechanisms for the varietal difference in grain chalkiness. The possible metabolic pathways affected by high temperature and their relevance to grain chalkiness are discussed.

Characteristics of Opaque and Translucent Parts of High Temperature Stressed Grains of Rice

“…They suggested that the textural properties of chalky grain were mainly caused by its relatively high hardness and chewiness. 11) Yamakawa et al (2007) 12) have also described less sticky texture of the high temperature-stressed chalky grains. Singh et al (2003) 6) described that the maximum force and chewiness of cooked rice of chalky grains was smaller than those of the translucent grains, while the chalky grains showed the higher conclusion temperature, Tc1, and the higher endothermic enthalpy, H1, of starch gelatinization by differential scanning calorimetry (DSC) compared with the translucent grains.…”

“…13,16) More precisely with an HPAEC-PAD technique, Umemoto et al 33) observed increased and decreased percentages of chains of DP 6-13 and DP 20-27 and 44-54, respectively, at lower temperatures during grain- 18) The chalkiness of ae mutant was overcome by transforming the wild-type BEIIb gene, 19) suggesting that the unusual expression of BEIIb is one of key factors causing the chalking of grain. However, Yamakawa et al (2007) 12) have mentioned that, judging from the data obtained using a series of high temperature tolerant and sensitive cultivars, the reduction of amylose content and the increase of long B chains of amylopectin by high temperature were not correlated to the grain chalkiness. Thus, the relevance of the starch fine structure to the chalkiness of grain under high temperature stress is obscure yet.…”

Endosperm Structure of White-Belly and White-Core Rice Grains Shown by Scanning Electron Microscopy

“…So far, the majority of studies with respect to grain chalkiness have been focused on starch, relating its accumulation or degradation to the formation of chalky tissue (Yamakawa et al, 2007;Fitzgerald et al, 2009). By contrast, the role of the other main component, the proteins, had been underestimated.…”

Changes in NMR Relaxation of Rice Grains, Kernel Quality and Physicochemical Properties in Response to a High Temperature after Flowering in Heat-Tolerant and Heat-Sensitive Rice Cultivars

“…In addition, the maximum viscosity and breakdown values were higher, and the final viscosity was low in grains grown at 30ºC. A high temperature was previously reported to enhance the protein content of rice grains (Honjyo, 1971) but decrease the amylose content (Chamura et al, 1979;Yamakawa et al, 2007), and to increase the maximum viscosity and breakdown values (Maeshige, 1984). Our results generally support these previous results, but the protein contents of the milled rice ranged from 5.3% to 5.6% and did not differ significantly between the two temperatures.…”