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

Kentaro Kaneko,Nanako Kuribayashi,Kimiko Itoh,Maiko Sasaki,Takeshi Shiraya,Yukiko Sasuga,Marouane Baslam,Toshiaki Mitsui,Takuya Inomata,Hiromu Suzuki

doi:10.1186/s12284-016-0100-y

Kentaro Kaneko, Nanako Kuribayashi + Show 8 more

Open Access

https://doi.org/10.1186/s12284-016-0100-y

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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.

Highlights

Global climate models predict an increase in global mean temperature and a higher frequency of intense heat spikes during this century
Together 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
Surface of the starch granules showed clearerosionwith multiple small pits suggesting an attack by α-amylases (Zakaria et al 2002; Iwasawa et al 2009); the suppression of α-amylase genes by RNA interference improved the appearance quality of rice grains ripened under heat stress (Hakata et al 2012)

Summary

Introduction

Global climate models predict an increase in global mean temperature and a higher frequency of intense heat spikes during this century. The abnormal high temperature during rice endosperm development and grain filling periods can change the chemical ingredients of rice caryopses such as starch and storage proteins and the contents of fatty acid, causing a decrease in grain yield, quality and, price. The surface of round-shaped starch granules in chalky grains caused by high-temperature stress had small pits occasionally (Tashiro and Wardlaw 1991). Surface of the starch granules showed clearerosionwith multiple small pits suggesting an attack by α-amylases (Zakaria et al 2002; Iwasawa et al 2009); the suppression of α-amylase genes by RNA interference improved the appearance quality of rice grains ripened under heat stress (Hakata et al 2012). Understanding of the mechanisms of grain chalking is indispensable to develop a strategy for reducing the high rate of chalky grains under the likely scenario of global warming (Lin et al 2014)

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