Integrated Analysis of the Effects of Cold and Dehydration on Rice Metabolites, Phytohormones, and Gene Transcripts

Abstract

Correlations between gene expression and metabolite/phytohormone levels under abiotic stress conditions have been reported for Arabidopsis (Arabidopsis thaliana). However, little is known about these correlations in rice (Oryza sativa 'Nipponbare'), despite its importance as a model monocot. We performed an integrated analysis to clarify the relationships among cold-and dehydrationresponsive metabolites, phytohormones, and gene transcription in rice. An integrated analysis of metabolites and gene expression indicated that several genes encoding enzymes involved in starch degradation, sucrose metabolism, and the glyoxylate cycle are upregulated in rice plants exposed to cold or dehydration and that these changes are correlated with the accumulation of glucose (Glc), fructose, and sucrose. In particular, high expression levels of genes encoding isocitrate lyase and malate synthase in the glyoxylate cycle correlate with increased Glc levels in rice, but not in Arabidopsis, under dehydration conditions, indicating that the regulation of the glyoxylate cycle may be involved in Glc accumulation under dehydration conditions in rice but not Arabidopsis. An integrated analysis of phytohormones and gene transcripts revealed an inverse relationship between abscisic acid (ABA) signaling and cytokinin (CK) signaling under cold and dehydration stresses; these stresses increase ABA signaling and decrease CK signaling. High levels of Oryza sativa 9-cis-epoxycarotenoid dioxygenase transcripts correlate with ABA accumulation, and low levels of Cytochrome P450 (CYP) 735A transcripts correlate with decreased levels of a CK precursor in rice. This reduced expression of CYP735As occurs in rice but not Arabidopsis. Therefore, transcriptional regulation of CYP735As might be involved in regulating CK levels under cold and dehydration conditions in rice but not Arabidopsis.Land plants must mount suitable responses to overcome the adverse effects of water stress caused by either drought or low-temperature conditions (Levitt, 1980). Among the external stresses, water stress is one of the most important limitations of crop productivity (Bartels and Sunkar, 2005). Discoveries of useful genes for molecular breeding using metabolomics and transcriptomics promise to facilitate the improvement of crop yields under water stress conditions. It is important to identify plant metabolites and transcripts that respond to water stress to determine the essential steps in molecular processes related to the effective adaptation of plants to stress conditions. Metabolomic and transcriptomic data have provided much information on the metabolite, phytohormone, and transcript networks that control plant growth and development. Studies using mass spectrometry (MS) -based metabolomic techniques have identified and characterized many stress-responsive metabolites

Abscisic acid and the key enzymes and genes in sucrose-to-starch conversion in rice spikelets in response to soil drying during grain filling

“…It would be possible that the ABA level was too high in rice spikelets under the SD or when a high concentration of ABA was applied. ABA above a normal level in the grains may have an adverse effect on grain filling as results of fast dehydration, reduction in cytokinin levels, depressions of gene expressions in starch biosynthesis, and a shortened grain filling period (Yang et al 2003;Zhu et al 2011;Farooq et al 2014;Maruyama et al 2014). and NCED5 (c) in superior (solid lines) and inferior (dotted lines) spikelets of rice.…”

A Drought-Inducible Transcription Factor Delays Reproductive Timing in Rice

“…Genome-wide investigations of transcription profiles have revealed that drought influences plant development and physiological responses by inducing hierarchical regulation of gene expression (Ding et al, 2012;Su et al, 2013;Huang et al, 2014;Maruyama et al, 2014). Several classes of transcription factors (TFs) play critical roles in orchestrating ABA-dependent or -independent drought responses Todaka et al, 2015).…”

The effects of drought on rice cultivation in sub-Saharan Africa and its mitigation: A review

“…In fact, the physiological and morphological reactions are based on these coordinated cellular responses which induce the expression of a large number of genes. In rice, more than 5,000 genes are up-regulated and more than 6,000 are down-regulated by drought stress (Maruyama et al, 2014). Wang et al (2011) conducted genome-wide gene expression profiling and detected 5,284 genes which were differentially expressed under drought stress, among which were under temporal and spatial regulation.…”