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Soil salinity is a major constraint that affects plant growth and development. Rice is a staple food for more than half of the human population but is extremely sensitive to salinity. Among the several known mechanisms, the ability of the plant to exclude cytosolic Na+ is strongly correlated with salinity stress tolerance in different plant species. This exclusion is mediated by the plasma membrane (PM) Na+/H+ antiporter encoded by Salt Overly Sensitive (SOS1) gene and driven by a PM H+-ATPase generated proton gradient. However, it is not clear to what extent this mechanism is operational in wild and cultivated rice species, given the unique rice root anatomy and the existence of the bypass flow for Na+. As wild rice species provide a rich source of genetic diversity for possible introgression of abiotic stress tolerance, we investigated physiological and molecular basis of salinity stress tolerance in Oryza species by using two contrasting pairs of cultivated (Oryza sativa) and wild rice species (Oryza alta and Oryza punctata). Accordingly, dose- and age-dependent Na+ and H+ fluxes were measured using a non-invasive ion selective vibrating microelectrode (the MIFE technique) to measure potential activity of SOS1-encoded Na+/H+ antiporter genes. Consistent with GUS staining data reported in the literature, rice accessions had (~4–6-fold) greater net Na+ efflux in the root elongation zone (EZ) compared to the mature root zone (MZ). Pharmacological experiments showed that Na+ efflux in root EZ is suppressed by more than 90% by amiloride, indicating the possible involvement of Na+/H+ exchanger activity in root EZ. Within each group (cultivated vs. wild) the magnitude of amiloride-sensitive Na+ efflux was higher in tolerant genotypes; however, the activity of Na+/H+ exchanger was 2–3-fold higher in the cultivated rice compared with their wild counterparts. Gene expression levels of SOS1, SOS2 and SOS3 were upregulated under 24 h salinity treatment in all the tested genotypes, with the highest level of SOS1 transcript detected in salt-tolerant wild rice genotype O. alta (~5–6-fold increased transcript level) followed by another wild rice, O. punctata. There was no significant difference in SOS1 expression observed for cultivated rice (IR1-tolerant and IR29-sensitive) under both 0 and 24 h salinity exposure. Our findings suggest that salt-tolerant cultivated rice relies on the cytosolic Na+ exclusion mechanism to deal with salt stress to a greater extent than wild rice, but its operation seems to be regulated at a post-translational rather than transcriptional level. [ABSTRACT FROM AUTHOR]

Na+ toxicity is one of the major physiological constraints imposed by salinity on plant performance. At the same time, Na+ uptake may be beneficial under some circumstances as an easily accessible inorganic ion that can be used for increasing solute concentrations and maintaining cell turgor. Two rice species, Oryza sativa (cultivated rice, salt-sensitive) and Oryza coarctata (wild rice, salt-tolerant), demonstrated different strategies in controlling Na+ uptake. Glasshouse experiments and gene expression analysis suggested that salt-treated wild rice quickly increased xylem Na+ loading for osmotic adjustment but maintained a non-toxic level of stable shoot Na+ concentration by increased activity of a high affinity K+ transporter HKT1;5 (essential for xylem Na+ unloading) and a Na+/H+ exchanger NHX (for sequestering Na+ and K+ into root vacuoles). Cultivated rice prevented Na+ uptake and transport to the shoot at the beginning of salt treatment but failed to maintain it in the long term. While electrophysiological assays revealed greater net Na+ uptake upon salt application in cultivated rice, O. sativa plants showed much stronger activation of the root plasma membrane Na+/H+ Salt Overly Sensitive 1 (SOS1) exchanger. Thus, it appears that wild rice limits passive Na+ entry into root cells while cultivated rice relies heavily on SOS1-mediating Na+ exclusion, with major penalties imposed by the existence of the "futile cycle" at the plasma membrane. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa), a staple crop for a substantial part of the world's population, is highly sensitive to soil salinity; however, some wild Oryza relatives can survive in highly saline environments. Sodium/hydrogen antiporter (NHX) family members contribute to Na+ homeostasis in plants and play a major role in conferring salinity tolerance. In this study, we analyzed the evolution of NHX family members using phylogeny, conserved domains, tertiary structures, expression patterns, and physiology of cultivated and wild Oryza species to decipher the role of NHXs in salt tolerance in Oryza. Phylogenetic analysis showed that the NHX family can be classified into three subfamilies directly related to their subcellular localization: endomembrane, plasma membrane, and tonoplast (vacuolar subfamily, vNHX1). Phylogenetic and structural analysis showed that vNHX1s have evolved from streptophyte algae (e.g., Klebsormidium nitens) and are abundant and highly conserved in all major land plant lineages, including Oryza. Moreover, we showed that tissue tolerance is a crucial trait conferring tolerance to salinity in wild rice species. Higher Na+ accumulation and reduced Na+ effluxes in leaf mesophyll were observed in the salt-tolerant wild rice species O. alta, O. latifolia, and O. coarctata. Among the key genes affecting tissue tolerance, expression of NHX1 and SOS1/NHX7 exhibited significant correlation with salt tolerance among the rice species and cultivars. This study provides insights into the evolutionary origin of plant NHXs and their role in tissue tolerance of Oryza species and facilitates the inclusion of this trait during the development of salinity-tolerant rice cultivars. [ABSTRACT FROM AUTHOR]

In plants, calcineurin B-like (CBL) proteins and their interacting protein kinases (CIPK) form functional complexes that transduce downstream signals to membrane effectors assisting in their adaptation to adverse environmental conditions. This study addresses the issue of the physiological role of CIPK9 in adaptive responses to salinity, osmotic stress, and K+ deficiency in rice plants. Whole-plant physiological studies revealed that Oscipk9 rice mutant lacks a functional CIPK9 gene and displayed a mildly stronger phenotype, both under saline and osmotic stress conditions. The reported difference was attributed to the ability of Oscipk9 to maintain significantly higher stomatal conductance (thus, a greater carbon gain). Oscipk9 plants contained much less K+ in their tissues, implying the role of CIPK9 in K+ acquisition and homeostasis in rice. Oscipk9 roots also showed hypersensitivity to ROS under conditions of low K+ availability suggesting an important role of H2O2 signalling as a component of plant adaptive responses to a low-K environment. The likely mechanistic basis of above physiological responses is discussed. [ABSTRACT FROM AUTHOR]

The domain of unknown function (DUF) superfamily encodes proteins of unknown functions in plants. Among them, DUF668 family members in plants possess a 29 amino-acid conserved domain, and this family has not been described previously. Here, we report this plant-specific novel DUF668 gene family containing 12 OsDUF668 genes in rice (Oryza sativa) and 91 DUF668s for the other seven plant species. In our study, DUF668 genes were present in both dicot and monocot plants, indicating that DUF668 is a conserved gene family that originated by predating the dicot–monocot divergence. Based on the gene structure and motif composition, the DUF668 family consists of two distinct clades, I and II in the phylogenetic tree. Remarkably, OsDUF668 genes clustered on the chromosomes merely show close phylogenetic relationships, suggesting that gene duplications or collinearity seldom happened. Cis-elements prediction display that over 80% of DUF668s contain phytohormone and light responsiveness factors. Further comprehensive experimental analyses of the OsDUF668 family are implemented in 22 different tissues, five hormone treatments, seven environmental factor stresses, and two pathogen-defense related stresses. The OsDUF668 genes express ubiquitously in analyzed rice tissues, and seven genes show tissue-specific high expression profiles. All OsDUF668s respond to drought, and some of Avr9/Cf-9 rapidly elicited genes resist to salt, wound, and rice blast with rapidly altered expression patterns. These findings imply that OsDUF668 is essential for drought-enduring and plant defense. Together, our results bring the important role of the DUF668 gene family in rice development and fitness to the fore. [ABSTRACT FROM AUTHOR]

Plant cell walls play a fundamental role in several ways, providing structural support for cells, resistance against pathogens and facilitating the communication between cells. The glycosyltransferase family 8 (GT8) is involved in the formation of the plant cell wall. However, the evolutionary relationship and the functional differentiation of this important gene family remain obscure in Gramineae crop genomes. In the present investigation, we identified 269 GT8 genes in the seven Gramineae representative crop genomes, namely, 33 in Hordeum vulgare, 37 in Brachypodium distachyon, 40 in Oryza sativa ssp. japonica, 41 in Oryza rufipogon, 36 in Setaria italica, 37 in Sorghum bicolor, and 45 in Zea mays. Phylogenetic analysis suggested that all identified GT8 proteins belonged to seven subfamilies: galacturonosyltransferase (GAUT), galacturonosyltransferase-like (GATL), GATL-related (GATR), galactinol synthase (GolS), and plant glycogenin-like starch initiation proteins A (PGSIP-A), PGSIP-B, and PGSIP-C. We estimated that the GAUT subfamily might be further divided into four subgroups (I–IV) due to differentiation of gene structures and expression patterns. Our orthogroup analysis identified 22 orthogroups with different sizes. Of these orthogroups, several orthogroups were lost in some species, such as S. italica and Z. mays. Moreover, lots of duplicate pairs and collinear pairs were discovered among these species. These results indicated that multiple duplication modes led to the expansion of this important gene family and unequal loss of orthogroups and subfamilies might have happened during the evolutionary process. RNA-seq, microarray analysis, and qRT-PCR analyses indicated that GT8 genes are critical for plant growth and development, and for stresses responses. We found that OsGolS1 was significantly up-regulated under salt stress, while OsGAUT21, OsGATL2, and OsGATL5 had remarkable up-regulation under cold stress. The current study highlighted the expansion and evolutionary patterns of the GT8 gene family in these seven Gramineae crop genomes and provided potential candidate genes for future salt- and cold- resistant molecular breeding studies in O. sativa. [ABSTRACT FROM AUTHOR]

Sugars are critical for plant growth and development as suppliers of carbon and energy, as signal molecules, or as solute molecules for osmotic homeostasis. Monosaccharide transporter (MST) genes are involved in various processes of plant growth and development as well as in response to abiotic stresses. However, the evolution and their roles of MST genes in growth and development and in coping with abiotic stresses in rice are poorly known. Here, we identified 64 MST genes in rice genome, which are classified into seven subfamilies: STP, PLT, AZT, ERD, pGlcT, INT, and XTPH. MST genes are not evenly distributed between chromosomes (Chrs) with a bias to Chr 3, 4, 7, and 11, which could be a result of duplication of fragments harboring MST genes. In total, 12 duplication events were found in the rice MST family, among which, two pairs were derived from fragmental duplications and ten pairs were from tandem duplications. The synonymous and nonsynonymous substitution rates of duplicate gene pairs demonstrated that the MST family was under a strong negative selection during the evolution process. Furthermore, a comprehensive expression analysis conducted in 11 different tissues, three abiotic stresses, five hormone treatments, and three sugar treatments revealed different expression patterns of MST genes and indicated diversified functions of them. Our results suggest that MST genes play important roles not only in various abiotic stresses but also in hormone and sugar responses. The present results will provide a vital insight into the functional divergence of the MST family in the future study. [ABSTRACT FROM AUTHOR]

Glycoside Hydrolase 3 (GH3), a member of the Auxin-responsive gene family, is involved in plant growth, the plant developmental process, and various stress responses. The GH3 gene family has been well-studied in Arabidopsis thaliana and Zea mays. However, the evolution of the GH3 gene family in Oryza species remains unknown and the function of the GH3 gene family in Oryza sativa is not well-documented. Here, a systematic analysis was performed in six Oryza species/subspecies, including four wild rice species and two cultivated rice subspecies. A total of 13, 13, 13, 13, 12, and 12 members were identified in O. sativa ssp. japonica, O. sativa ssp. indica, Oryza rufipogon, Oryza nivara, Oryza punctata, and Oryza glumaepatula, respectively. Gene duplication events, structural features, conserved motifs, a phylogenetic analysis, chromosome locations, and Ka/Ks ratios of this important family were found to be strictly conservative across these six Oryza species/subspecies, suggesting that the expansion of the GH3 gene family in Oryza species might be attributed to duplication events, and this expansion could occur in the common ancestor of Oryza species, even in common ancestor of rice tribe (Oryzeae) (23.07~31.01 Mya). The RNA-seq results of different tissues displayed that OsGH3 genes had significantly different expression profiles. Remarkably, the qRT-PCR result after NaCl treatment indicated that the majority of OsGH3 genes play important roles in salinity stress, especially OsGH3-2 and OsGH3-8. This study provides important insights into the evolution of the GH3 gene family in Oryza species and will assist with further investigation of OsGH3 genes' functions under salinity stress. [ABSTRACT FROM AUTHOR]