Characterization of the PaHAK Gene and Its Expression During the In Vitro Seed Germination of Two Botanical Avocado Varieties Under Saline Stress.

Soil salinity is one of the main challenges that modern agriculture faces. Avocado, which is classified as a glycophyte, is very sensitive to salt stress. There are botanical varieties of avocado that differ in their salt tolerance.

Combining Genetic and Transcriptomic Approaches to Identify Transporter-Coding Genes as Likely Responsible for a Repeatable Salt Tolerance QTL in Citrus.

The excessive accumulation of chloride (Cl) in leaves due to salinity is frequently related to decreased yield in citrus. Two salt tolerance experiments to detect quantitative trait loci (QTLs) for leaf concentrations of Cl, Na, and other traits using the same reference progeny derived from the salt-tolerant Cleopatra mandarin () and the disease-resistant donor were performed with the aim to identify repeatable QTLs that regulate leaf Cl (and/or Na) exclusion across independent experiments in citrus, as well as potential candidate genes involved. A repeatable QTL controlling leaf Cl was detected in chromosome 6 (), where 23 potential candidate genes coding for transporters were identified using the genome as reference.

HKT1;1 and HKT1;2 Na Transporters from Play Different Roles in the Plant Na Distribution under Salinity.

Salt tolerance is a target trait in plant science and tomato breeding programs. Wild tomato accessions have been often explored for this purpose. Since shoot Na/K is a key component of salt tolerance, RNAi-mediated knockdown isogenic lines obtained for alleles encoding both class I Na transporters HKT1;1 and HKT1;2 were used to investigate the silencing effects on the Na and K contents of the xylem sap, and source and sink organs of the scion, and their contribution to salt tolerance in all 16 rootstock/scion combinations of non-silenced and silenced lines, under two salinity treatments.

Role of Na transporters HKT1;1 and HKT1;2 in tomato salt tolerance. I. Function loss of cheesmaniae alleles in roots and aerial parts.

We analyzed the physiological impact of function loss on cheesmaniae alleles at the HKT1;1 and HKT1;2 loci in the roots and aerial parts of tomato plants in order to determine the relative contributions of each locus in the different tissues to plant Na/K homeostasis and subsequently to tomato salt tolerance. We generated different reciprocal rootstock/scion combinations with non-silenced, single RNAi-silenced lines for ScHKT1;1 and ScHKT1;2, as well as a silenced line at both loci from a near isogenic line (NIL14), homozygous for the Solanum cheesmaniae haplotype containing both HKT1 loci and subjected to salinity under natural greenhouse conditions. Our results show that salt treatment reduced vegetative growth and altered the Na/K ratio in leaves and flowers; negatively affecting fruit production, particularly in graft combinations containing single silenced ScHKT1;2- and double silenced ScHKT1;1/ScHKT1;2 lines when used as scion.

Na transporter HKT1;2 reduces flower Na content and considerably mitigates the decline in tomato fruit yields under saline conditions.

Genes encoding HKT1-like Na transporters play a key role in the salinity tolerance mechanism in Arabidopsis and other plant species by retrieving Na from the xylem of different organs and tissues. In this study, we investigated the role of two HKT1;2 allelic variants in tomato salt tolerance in relation to vegetative growth and fruit yield in plants subjected to salt treatment in a commercial greenhouse under real production conditions. We used two near-isogenic lines (NILs), homozygous for either the Solanum lycopersicum (NIL17) or S.

The sodium transporter encoded by the HKT1;2 gene modulates sodium/potassium homeostasis in tomato shoots under salinity.

Excessive soil salinity diminishes crop yield and quality. In a previous study in tomato, we identified two closely linked genes encoding HKT1-like transporters, HKT1;1 and HKT1;2, as candidate genes for a major quantitative trait locus (kc7.1) related to shoot Na /K homeostasis - a major salt tolerance trait - using two populations of recombinant inbred lines (RILs).

Heterologous expression of the yeast HAL5 gene in tomato enhances salt tolerance by reducing shoot Na+ accumulation in the long term.

For salt tolerance to be achieved in the long-term plants must regulate Na(+)/K(+) homeostasis over time. In this study, we show that the salt tolerance induced by overexpression of the yeast HAL5 gene in tomato (Solanum lycopersicum) was related to a lower leaf Na(+) accumulation in the long term, by reducing Na(+) transport from root to shoot over time regardless of the severity of salt stress. Furthermore, maintaining Na(+)/K(+) homeostasis over time was associated with changes in the transcript levels of the Na(+) and K(+) transporters such as SlHKT1;2 and SlHAK5.

Two closely linked tomato HKT coding genes are positional candidates for the major tomato QTL involved in Na+ /K+ homeostasis.

The location of major quantitative trait loci (QTL) contributing to stem and leaf [Na(+) ] and [K(+) ] was previously reported in chromosome 7 using two connected populations of recombinant inbred lines (RILs) of tomato. HKT1;1 and HKT1;2, two tomato Na(+) -selective class I-HKT transporters, were found to be closely linked, where the maximum logarithm of odds (LOD) score for these QTLs located. When a chromosome 7 linkage map based on 278 single-nucleotide polymorphisms (SNPs) was used, the maximum LOD score position was only 35 kb from HKT1;1 and HKT1;2.

Involvement of SlSOS2 in tomato salt tolerance.

The Ca(2+)-dependent SOS pathway has emerged as a key mechanism in the homeostasis of Na(+) and K(+) under saline conditions. We recently identified and functionally characterized by complementation studies in yeast and Arabidopsis the gene encoding the calcineurin-interacting protein kinase of the SOS pathway in tomato, SlSOS2.(1) We also show evidences on the biotechnological potential of SlSOS2 conferring salt tolerance to transgenic tomato.

Overexpression of SlSOS2 (SlCIPK24) confers salt tolerance to transgenic tomato.

The Ca(2+)-dependent SOS pathway has emerged as a key mechanism in the homeostasis of Na(+) and K(+) under saline conditions. We have identified and functionally characterized the gene encoding the calcineurin-interacting protein kinase of the SOS pathway in tomato, SlSOS2. On the basis of protein sequence similarity and complementation studies in yeast and Arabidopsis, it can be concluded that SlSOS2 is the functional tomato homolog of Arabidopsis AtSOS2 and that SlSOS2 operates in a tomato SOS signal transduction pathway.

The Na(+)/H(+) exchanger SOS1 controls extrusion and distribution of Na(+) in tomato plants under salinity conditions.

Maintaining a high K(+)/Na(+) ratio in the cell cytosol, along with the transport processes implicated in the xylem and phloem loading/unloading of Na(+) in plants (long-distance transport) are key aspects in plant salt tolerance. The Ca(2+)-dependent SOS pathway regulating Na(+) and K(+) homeostasis and long-distance Na(+) transport has been reported in Arabidopsis. However, Arabidopsis might not be the best model to analyze the involvement of the SOS pathway in long-distance Na(+) transport due to the very short stem of these plants which do not allow a precise dissection of the relative content of Na(+) in stem versus leaf.

The plasma membrane Na+/H+ antiporter SOS1 is essential for salt tolerance in tomato and affects the partitioning of Na+ between plant organs.

We have identified a plasma membrane Na(+)/H(+) antiporter gene from tomato (Solanum lycopersicum), SlSOS1, and used heterologous expression in yeast to confirm that SlSOS1 was the functional homolog of AtSOS1. Using post-transcriptional gene silencing, we evaluated the role played by SlSOS1 in long-distance Na(+) transport and salt tolerance of tomato. Tomato was used because of its anatomical structure, more complex than that of Arabidopsis, and its agricultural significance.

Heterologously expressed protein phosphatase calcineurin downregulates plant plasma membrane H+-ATPase activity at the post-translational level.

To investigate the effects of calcineurin expression on cellular ion homeostasis in plants, we have obtained a transgenic cell culture of tomato, expressing constitutively activated yeast calcineurin. Transgenic cells exhibited reduced growth rates and proton extrusion activity in vivo. We show that reduction of plasma membrane H+-ATPase activity by expression of calcineurin is the basis for the observed phenotypes.

A novel intracellular K+/H+ antiporter related to Na+/H+ antiporters is important for K+ ion homeostasis in plants.

In this study we have identified the first plant K+/H+ exchanger, LeNHX2 from tomato (Lycopersicon esculentum Mill. cv. Moneymaker), which is a member of the intracellular NHX exchanger protein family.

Involvement of endogenous salicylic acid content, lipoxygenase and antioxidant enzyme activities in the response of tomato cell suspension cultures to NaCl.

•   The effects of salt stress and adaptation on salicylic acid (SA) content and on antioxidant and lipoxygenase (LOX) enzyme activities were studied in tomato (Lycopersicon esculentum cv. Pera) cells. •   NaCl-adapted cells were obtained from calli adapted to 100 mm NaCl by successive subcultures in medium supplemented with 100 mm NaCl.