Abstract
A near-isogenic line (NIL) DC90 which was generated by introgressing a wild rice (Oryza rufipogon Griff.) locus CTS-12 into the 9311(Oryza sativa L. ssp. indica) background confers chilling tolerance phenotype. Here, our pilot trials showed that chilling tolerance was positively correlated with abscisic acid (ABA) biosynthesis. To understand how CTS-12 mediated the ABA-dependent multi-levels of regulation, the integration of transcriptomic and metabolomic profiling using the two-way orthogonal projections to latent structures (O2PLS) and discriminant analysis (OPLS-DA) modeling was performed to investigate the mechanisms underlying chilling tolerance. Our results revealed that metabolic shifts, including the activation of stachyose biosynthesis, amino acid metabolism pathways, phenylpropanoid/flavonoid biosynthesis, ABA biosynthesis, and perturbation of glycolysis, occurred under chilling treatment; in the recovery period, glutamate-related pathways, β-alanine biosynthesis and degradation, and serotonin biosynthesis pathways were differentiated between 9311 and DC90. Particularly, the differentially accumulated metabolites (DAMs) and differentially expressed genes (DEGs), including galactinol, β-alanine, glutamate, naringenin, serotonin, ABA, and LOC_Os03g44380 (9-cis-epoxycarotenoid dioxygenase 3, OsNCED3), might be involved in the chilling tolerance variation of 9311 and DC90. CRISPR/Cas9-edited OsNCED3 resulted in chilling sensitive of japonica rice ZH11, demonstrating the involvement of ABA pathway in chilling stress response. In addition, chilling tolerance of rice was associated with the balance of water uptake and loss that was modulated by stomatal movement under chilling stress. Therefore, we speculated that the CTS-12-mediated ABA signaling pathway leads to transcriptional regulation of chilling-responsive genes and, in turn, triggers metabolic shifts to coordinately regulate the stomatal movement of guard cells. The results of this study improve our understanding of the multilevel regulation of wild rice in response to chilling stress.
Highlights
Higher plants are sessile and usually adopt the ‘overcome’ strategy upon encountering any extreme environmental stresses, in contrast to animals, which preferentially opt for the avoidance of unfavorable circumstances
Our results suggest that the differentially accumulated metabolites (DAMs) and differentially expressed genes (DEGs), including galactinol, β-alanine, glutamate, naringenin, serotonin, abscisic acid (ABA), and LOC_Os03g44380, might be involved in the chilling tolerance variation of 9311 and DC90
The treatment of chilling-treated seedlings with Na2WO4, an inhibitor of ABA biosynthesis, resulted in reduced chilling tolerance of DC90 (Figures 1B,C). These results suggested that ABA biosynthesis might be impaired in 9311 and results in a chilling sensitive phenotype
Summary
Higher plants are sessile and usually adopt the ‘overcome’ strategy upon encountering any extreme environmental stresses, in contrast to animals, which preferentially opt for the avoidance of unfavorable circumstances. Recent advances in our understanding of ABA signal transduction suggest that three protein classes, pyracbactin resistance/pyracbactin resistance-like/regulatory component of ABA receptor (PYR/PYL/RCARs), are ABA receptors. In this signaling pathway, protein phosphatase 2Cs (PP2Cs) and sucrose non-fermenting 1 (SNF1)-related protein kinase 2s (SnRK2s), in particular, open stomata 1 (OST1)/SnRK2.6, act as negative and positive regulators, respectively (Yoshida et al, 2006; Park et al, 2009; Umezawa et al, 2009). In the ABA-mediated stomatal movement signaling pathway, ROS, NO, and Ca2+ act as a key convergence point for the regulation of stomatal closure. The increased levels of ROS, NO, or Ca2+ in guard cells trigger multiple events in either downstream or upstream processes (Agurla and Raghavendra, 2016)
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