Population differentiation within Festuca rubra L. with regard to soil salinity and soil water

Summary Seed and transplanted adult plants from populations of Festuca rubra, collected from inland, salt-marsh and sand-dune sites were grown on culture solution with added sodium chloride. The growth of the populations of the three habitats was reduced differentially by salt. The salt marsh ecotype Festuca rubra ssp. litoralis was only slightly affected and the inland ecotype F. rubra ssp. rubra was severely retarded at 60 mM NaCl. The dune ecotype F. rubra ssp. arenaria had an intermediate tolerance. The tolerant ecotypes accumulated less sodium chloride as compared to the sensitive ecotype, suggesting that salt tolerance is caused in part by salt exclusion.In addition, the dune ecotype F.r. arenaria appeared to be more drought tolerant than the salt marsh ecotype. Abscission of salt-saturated leaves does not function as an adaptation to salinity in Festuca rubra.All three ecotypes accumulated proline with increased salinity. The response was most pronounced in the drought tolerant F.r. arenaria, indicating that proline accumulation is a response to osmotic stress rather than to ion-specific effects of salinity. The observed differences in salt tolerance may be explained by differential sensitivity to toxic effects of sodium chloride.The occurrence on a beach plain of closely adjacent populations of F.r. arenaria and F.r. litoralis, differing markedly in salt tolerance, is briefly discussed.     

OsMPK4 promotes phosphorylation and degradation of IPA1 in response to salt stress to confer salt tolerance in rice

Salt stress adversely affects plant growth, development, and crop yield. Rice (Oryza sativa L.) is one of the most salt-sensitive cereal crops, especially at the early seedling stage. Mitogen-activated protein kinase (MAPK/MPK) cascades have been shown to play critical roles in salt response in Arabidopsis. However, the roles of the MPK cascade signaling in rice salt response and substrates of OsMPK remain largely unknown. Here, we report that the salt-induced OsMPK4-Ideal Plant Architecture 1 (IPA1) signaling pathway regulates the salt tolerance in rice. Under salt stress, OsMPK4 could interact with IPA1 and phosphorylate IPA1 at Thr180, leading to degradation of IPA1. Genetic evidence shows that IPA1 is a negative regulator of salt tolerance in rice, whereas OsMPK4 promotes salt response in an IPA1-dependent manner. Taken together, our results uncover an OsMPK4-IPA1 signal cascade that modulates the salt stress response in rice and sheds new light on the breeding of salt-tolerant rice varieties.     

meta-Tyrosine in Festuca rubra ssp. commutata (Chewings fescue) is synthesized by hydroxylation of phenylalanine

m-Tyrosine is a non-protein amino acid that is structurally similar to the common protein amino acids p-tyrosine and phenylalanine. Copious amounts of m-tyrosine can be found in root exudates of the fine fescue cultivar, Festuca rubra L. ssp. commutata (Chewings fescue). The phytotoxicity of m-tyrosine may contribute to the allelopathic potential of F. rubra. m-Tyrosine in Euphorbia myrsinites (donkey-tail spurge), was previously shown to be synthesized via transamination of m-hydroxyphenylpyruvate. Here we show that m-tyrosine biosynthesis in F. rubra occurs through direct hydroxylation of phenylalanine in the root tips, perhaps through the activity of a cytochrome P450 enzyme. Hence, E. myrsinites and F. rubra, the only two plant species known to produce m-tyrosine, use distinct biosynthetic pathways that likely arose independently in evolutionary history.     

A Novel Little Membrane Protein Confers Salt Tolerance in Rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Plasma membrane proteins play critical roles in sensing and responding abiotic and biotic stresses in plants. In the present study, we characterized a previously unknown gene stress associated little protein 1 (SALP1) encoding a plasma membrane protein. SALP1, a small and plant-specific membrane protein, contains only 74 amino acid residues. SALP1 was constitutively expressed in various rice tissues while highly expressed in roots, leaf blade, and immature panicles. Expression analysis indicated that SALP1 was induced by various abiotic stresses and abscisic acid (ABA). Subcellular localization assay indicated that SALP1 was localized on plasma membrane in rice protoplast cells. Overexpressing of SALP1 in rice improved salt tolerance through increasing free proline contents and the expression level of OsP5CS gene, and balancing ion contents under salt stress. Moreover, SALP1 transgenic rice showed reduced sensitivity to ABA treatment, and expression level of SALP1 is not altered by ABI5-like 1 protein. Conclusively, SALP1, a novel membrane protein, is involved in salt tolerance through an ABA-independent signaling pathway in rice.