Proteomic and Glycomic Characterization of Rice Chalky Grains Produced Under Moderate and High-temperature Conditions in Field System

Abstract

BackgroundGlobal climate models predict an increase in global mean temperature and a higher frequency of intense heat spikes during this century. Cereals such as rice (Oryza sativa L.) are more susceptible to heat stress, mainly during the gametogenesis and flowering stages. During periods of high temperatures, grain filling often causes serious damage to the grain quality of rice and, therefore, yield losses. While the genes encoding enzymes involved in carbohydrate metabolism of chalky grains have been established, a significant knowledge gap exists in the proteomic and glycomic responses to warm temperatures in situ. Here, we studied the translucent and opaque characters of high temperature stressed chalky grains of 2009 and 2010 (ripening temperatures: 24.4 and 28.0 °C, respectively).ResultsAppearance of chalky grains of both years showed some resemblance, and the high-temperature stress of 2010 remarkably extended the chalking of grain. Scanning electron microscopic observation showed that round-shaped starch granules with numerous small pits were loosely packed in the opaque part of the chalky grains. Proteomic analyzes of rice chalky grains revealed deregulations in the expression of multiple proteins implicated in diverse metabolic and physiological functions, such as protein synthesis, redox homeostasis, lipid metabolism, and starch biosynthesis and degradation. The glycomic profiling has shown slight differences in chain-length distributions of starches in the grains of 2009-to-2010. However, no significant changes were observed in the chain-length distributions between the translucent and opaque parts of perfect and chalky grains in both years. The glucose and soluble starch contents in opaque parts were increased by the high-temperature stress of 2010, though those in perfect grains were not different regardless of the environmental changes of 2009-to-2010.ConclusionTogether with previous findings on the increased expression of α-amylases in the endosperm, these results suggested that unusual starch degradation rather than starch synthesis is involved in occurring of chalky grains of rice under the high-temperature stress during grain filling period.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-016-0100-y) contains supplementary material, which is available to authorized users.

High Temperature-Induced Expression of Rice α-Amylases in Developing Endosperm Produces Chalky Grains

“…These responses suggest that activation of starch degradation occurs along with the repression of starch biosynthesis in rice grains exposed to high temperature, and counteracts the deposition of starch in the maturing endosperm. Consistently, the traces of starch degradation were observed as small pits and holes on the surface of immature starch granules in the chalky part of grains ripened at high temperature ( Zakaria et al, 2002 ; Tsutsui et al, 2013 ; Kaneko et al, 2016 ).…”

“…Therefore, it is unclear which α-amylases function to generate chalky grains at high temperatures. Moreover, whether the site where the chalkiness occurs in high temperature conditions is consistently associated with the expression pattern of α-amylase remains to be determined, although a previous proteomic study revealed that high temperature promoted the accumulation of α-amylase proteins, namely Amy3D and Amy3E, in mature grains ( Kaneko et al, 2016 ).…”

FLOURY ENDOSPERM11‐2 encodes plastid HSP70‐2 involved with the temperature‐dependent chalkiness of rice (Oryza sativa L.) grains

“…Lin et al (2017) used a notched-belly rice mutant, which has a translucent upper half and a chalky bottom half within a single grain, and detected 363 proteins that were expressed differently between the two parts. Kaneko et al (2016) demonstrated that some isoforms of a-amylase expression and soluble starch and glucose accumulation increased in chalky grains. The molecular mechanism explaning the relationship between heat and chalkiness is not fully understood, however.…”

Dissection of brassinosteroid-regulated proteins in rice embryos during germination by quantitative proteomics

“…Therefore, BR-regulated ribosomal protein abundance may play an important role in orchestrate seed germination process. Besides seed germination, proteomic studies indicated that protein-synthesis-related proteins and ribosomal proteins also played important roles in forming rice chalky grains by modulating energy and metabolic pathways 50 51 . Recently, study also showed that BR involved in the energy metabolism regulation under stress conditions by inducing de novo protein synthesis 52 .…”