The physiological and molecular mechanisms of tolerance to osmotic and ionic components of salinity stress are reviewed at the cellular, organ, and whole-plant level. Plant growth responds to salinity in two phases: a rapid, osmotic phase that inhibits growth of young leaves, and a slower, ionic phase that accelerates senescence of mature leaves. Plant adaptations to salinity are of three distinct types: osmotic stress tolerance, Na + or Cl − exclusion, and the tolerance of tissue to accumulated Na + or Cl − . Our understanding of the role of the HKT gene family in Na + exclusion from leaves is increasing, as is the understanding of the molecular bases for many other transport processes at the cellular level. However, we have a limited molecular understanding of the overall control of Na + accumulation and of osmotic stress tolerance at the whole-plant level. Molecular genetics and functional genomics provide a new opportunity to synthesize molecular and physiological knowledge to improve the salinity tolerance of plants relevant to food production and environmental sustainability.

https://rodas5.us.es/file/c2a700e9-8b4a-1970-d343-4a269c302970/1/estres_salino_bibliografia_scorm.zip/files/estres_salino_bibliografia.pdf

Mechanisms of salinity tolerance

▪ Abstract Plant responses to salinity stress are reviewed with emphasis on molecular mechanisms of signal transduction and on the physiological consequences of altered gene expression that affect biochemical reactions downstream of stress sensing. We make extensive use of comparisons with model organisms, halophytic plants, and yeast, which provide a paradigm for many responses to salinity exhibited by stress-sensitive plants. Among biochemical responses, we emphasize osmolyte biosynthesis and function, water flux control, and membrane transport of ions for maintenance and re-establishment of homeostasis. The advances in understanding the effectiveness of stress responses, and distinctions between pathology and adaptive advantage, are increasingly based on transgenic plant and mutant analyses, in particular the analysis of Arabidopsis mutants defective in elements of stress signal transduction pathways. We summarize evidence for plant stress signaling systems, some of which have components analogous to t...

Plant cellular and molecular responses to high salinity.

Roles of glycine betaine and proline in improving plant abiotic stress resistance

Abiotic stresses, such as drought, salinity, extreme temperatures, chemical toxicity and oxidative stress are serious threats to agriculture and the natural status of the environment. Increased salinization of arable land is expected to have devastating global effects, resulting in 30% land loss within the next 25 years, and up to 50% by the year 2050. Therefore, breeding for drought and salinity stress tolerance in crop plants (for food supply) and in forest trees (a central component of the global ecosystem) should be given high research priority in plant biotechnology programs. Molecular control mechanisms for abiotic stress tolerance are based on the activation and regulation of specific stress-related genes. These genes are involved in the whole sequence of stress responses, such as signaling, transcriptional control, protection of membranes and proteins, and free-radical and toxic-compound scavenging. Recently, research into the molecular mechanisms of stress responses has started to bear fruit and, in parallel, genetic modification of stress tolerance has also shown promising results that may ultimately apply to agriculturally and ecologically important plants. The present review summarizes the recent advances in elucidating stress-response mechanisms and their biotechnological applications. Emphasis is placed on transgenic plants that have been engineered based on different stress-response mechanisms. The review examines the following aspects: regulatory controls, metabolite engineering, ion transport, antioxidants and detoxification, late embryogenesis abundant (LEA) and heat-shock proteins.

/pdf/plant-responses-to-drought-salinity-and-extreme-temperatures-2t6tpv484r.pdf

Plant responses to drought, salinity and extreme temperatures: towards genetic engineering for stress tolerance

Na+ Tolerance and Na+ Transport in Higher Plants

In Arabidopsis thaliana (ecotype Columbia) mutant line AS11, an EMS-induced mutation at a locus on chromosome II results in a reduced diacylglycerol acyltransferase (DGAT; EC 2.3.1.20) activity, reduced seed triacylglycerol, an altered seed fatty acid composition, and delayed seed development. A mutation has been identified in AS11 in a gene, which we designated as TAG1, that encodes a protein with an amino acid sequence which is similar to a recently reported mammalian DGAT, and, to a lesser extent, to acyl CoA:cholesterol acyltransferases. Molecular analysis revealed that the mutant allele in AS11 has a 147 bp insertion located at the central region of intron 2. At the RNA level, an 81 bp insertion composed entirely of an exon 2 repeat was found in the transcript. While the seed triacylglycerol content is reduced by the lesion in AS11, there is no apparent effect on sterol ester content in the mutant seed. The TAG1 cDNA was over-expressed in yeast, and its activity as a microsomal DGAT confirmed. Therefore, the TAG1 locus encodes a diacylglycerol acyltransferase, and the insertion mutation in the TAG1 gene in mutant AS11 results in its altered lipid phenotype.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-313x.1999.00555.x

The Arabidopsis thaliana TAG1 mutant has a mutation in a diacylglycerol acyltransferase gene

Glycinebetaine (betaine) affords osmoprotection in bacteria, plants and animals, and protects cell components against harsh conditions in vitro. This and a compelling body of other evidence have encouraged the engineering of betaine production in plants lacking it. We have installed the metabolic step for oxidation of choline, a ubiquitous substance, to betaine in three diverse species, Arabidopsis, Brassica napus, and tobacco (Nicotiana tabacum), by constitutive expression of a bacterial choline oxidase gene. The highest levels of betaine in independent transgenics were 18.6, 12.8, and 13 μmol g−1 dry weight, respectively, values 10- to 20-fold lower than the levels found in natural betaine producers. However, choline-fed transgenic plants synthesized substantially more betaine. Increasing the choline supplementation further enhanced betaine synthesis, up to 613 μmol g−1 dry weight in Arabidopsis, 250 μmol g−1 dry weight in B. napus, and 80 μmol g−1 dry weight in tobacco. These studies demonstrate the need to enhance the endogenous choline supply to support accumulation of physiologically relevant amounts of betaine. A moderate stress tolerance was noted in some but not all betaine-producing transgenic lines based on relative shoot growth. Furthermore, the responses to stresses such as salinity, drought, and freezing were variable among the three species.

Genetic engineering of glycinebetaine production toward enhancing stress tolerance in plants: metabolic limitations.

Flowering plants display a remarkable range of inflorescence architecture, and pedicel characteristics are one of the key contributors to this diversity. However, very little is known about the genes or the pathways that regulate pedicel development. The brevipedicellus (bp) mutant of Arabidopsis thaliana displays a unique phenotype with defects in pedicel development causing downward-pointing flowers and a compact inflorescence architecture. Cloning and molecular analysis of two independent mutant alleles revealed that BP encodes the homeodomain protein KNAT1, a member of the KNOX family. bp-1 is a null allele with deletion of the entire locus, whereas bp-2 has a point mutation that is predicted to result in a truncated protein. In both bp alleles, the pedicels and internodes were compact because of fewer cell divisions; in addition, defects in epidermal and cortical cell differentiation and elongation were found in the affected regions. The downward-pointing pedicels were produced by an asymmetric effect of the bp mutation on the abaxial vs. adaxial sides. Cell differentiation, elongation, and growth were affected more severely on the abaxial than adaxial side, causing the change in the pedicel growth angle. In addition, bp plants displayed defects in cell differentiation and radial growth of the style. Our results show that BP plays a key regulatory role in defining important aspects of the growth and cell differentiation of the inflorescence stem, pedicel, and style in Arabidopsis.

http://www.pnas.org/content/99/7/4730.full.pdf

The homeobox gene BREVIPEDICELLUS is a key regulator of inflorescence architecture in Arabidopsis

For a long time it has been believed that lignification has an important role in host defense against pathogen invasion. Recently, by using an RNAi gene-silencing assay we showed that monolignol biosynthesis plays a critical role in cell wall apposition (CWA)-mediated defense against powdery mildew fungus penetration into diploid wheat. Silencing monolignol genes led to super-susceptibility of wheat leaf tissues to an appropriate pathogen, Blumeria graminis f. sp. tritici (Bgt), and compromised penetration resistance to a non-appropriate pathogen, B. graminis f. sp. hordei. Autofluorescence of CWA regions was reduced significantly at the fungal penetration sites in silenced cells. Our work indicates an important role for monolignol biosynthetic genes in effective CWA formation against pathogen penetration. In this addendum, we show that silencing of monolignol genes also compromised penetration resistant to Bgt in a resistant wheat line. In addition, we discuss possible insights into how lignin biosynthesis contributes to host defense.

Role of lignification in plant defense

Membrane-bound glycerol-3-phosphate acyltransferase (GPAT; EC 2.3.1.15) mediates the initial step of glycerolipid biosynthesis in the extraplastidic compartments of plant cells. Here, we report the molecular characterization of a novel GPAT gene family from Arabidopsis, designated AtGPAT. The corresponding polypeptides possess transmembrane domains and GPAT activity when expressed heterologously in a yeast lipid mutant. The functional significance of one isoform, AtGPAT1, is the focus of the present study. Disruption of the AtGPAT1 gene causes a massive pollen development arrest, and subsequent introduction of the gene into the mutant plant rescues the phenotype, illustrating a pivotal role for AtGPAT1 in pollen development. Microscopic examinations revealed that the gene lesion results in a perturbed degeneration of the tapetum, which is associated with altered endoplasmic reticulum profiles and reduced secretion. In addition to the sporophytic effect, AtGPAT1 also exerts a gametophytic effect on pollen performance, as the competitive ability of a pollen grain to pollinate is dependent on the presence of an AtGPAT1 gene. Deficiency in AtGPAT1 correlates with several fatty acid composition changes in flower tissues and seeds. Unexpectedly, however, a loss of AtGPAT1 causes no significant change in seed oil content.

Arabidopsis AtGPAT1 , a Member of the Membrane-Bound Glycerol-3-Phosphate Acyltransferase Gene Family, Is Essential for Tapetum Differentiation and Male Fertility

Gopalan Selvaraj

Papers

The Arabidopsis thaliana TAG1 mutant has a mutation in a diacylglycerol acyltransferase gene

Genetic engineering of glycinebetaine production toward enhancing stress tolerance in plants: metabolic limitations.

The homeobox gene BREVIPEDICELLUS is a key regulator of inflorescence architecture in Arabidopsis

Role of lignification in plant defense

Arabidopsis AtGPAT1 , a Member of the Membrane-Bound Glycerol-3-Phosphate Acyltransferase Gene Family, Is Essential for Tapetum Differentiation and Male Fertility