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Summary Under salinity, Vitis spp. rootstocks can mediate salt (NaCl) exclusion from grafted V. vinifera scions enabling higher grapevine yields and production of superior wines with lower salt content. Until now, the genetic and mechanistic elements controlling sodium (Na+) exclusion in grapevine were unknown. Using a cross between two Vitis interspecific hybrid rootstocks, we mapped a dominant quantitative trait locus (QTL) associated with leaf Na+ exclusion (NaE) under salinity stress. The NaE locus encodes six high-affinity potassium transporters (HKT). Transcript profiling and functional characterization in heterologous systems identified VisHKT1;1 as the best candidate gene for controlling leaf Na+ exclusion. We characterized four proteins encoded by unique VisHKT1;1 alleles from the parents, and revealed that the dominant HKT variants exhibit greater Na+ conductance with less rectification than the recessive variants. Mutagenesis of VisHKT1;1 and TaHKT1.5-D from bread wheat, demonstrated that charged amino acid residues in the eighth predicted transmembrane domain of HKT proteins reduces inward Na+ conductance, and causes inward rectification of Na+ transport. The origin of the recessive VisHKT1;1 alleles was traced to V. champinii and V. rupestris. We propose that the genetic and functional data presented here will assist with breeding Na+-tolerant grapevine rootstocks.

Under salinity, Vitis spp. rootstocks can mediate salt (NaCl) exclusion from grafted V. vinifera scions enabling higher grapevine yields and production of superior wines with lower salt content. Until now, the genetic and mechanistic elements controlling sodium (Na

Potted grapevines of 140 Ruggeri (Vitis berlandieri × Vitis rupestris), a good Cl(-) excluder, and K 51-40 (Vitis champinii × Vitis riparia 'Gloire'), a poor Cl(-) excluder, and of a family obtained by crossing the two genotypes, were used to examine the inheritance of Cl(-) exclusion. Rooted leaves were then used to further investigate the mechanism for Cl(-) exclusion in 140 Ruggeri. In both a potting mix trial (plants watered with 50 mM Cl(-)) and a solution culture trial (plants grown in 25 mM Cl(-)), the variation in Cl(-) accumulation was continuous, indicating multiple rather than single gene control for Cl(-) exclusion between hybrids within the family. Upper limits of 42% and 35% of the phenotypic variation in Cl(-) concentration could be attributed to heritable sources in the potting mix and solution culture trials, respectively. Chloride transport in roots of rooted leaves of both genotypes appeared to be via the symplastic pathway, since addition of 8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS), an apoplastic tracer, revealed no obvious PTS fluorescence in the laminae of either genotype, despite significant accumulation of Cl(-) in laminae of K 51-40 during the PTS uptake period. There was no significant difference in either unidirectional (36)Cl(-) flux (10 min) or (36)Cl(-) uptake (3 h) into roots of rooted leaves exposed to 5, 10, or 25 mM Cl(-). However, the percentage of (36)Cl(-) transported to the lamina (3 h) was significantly lower in 140 Ruggeri than in K 51-40, supporting reduced Cl(-) loading into xylem and implicating the root stele in the Cl(-) exclusion mechanism.

Background Salt tolerance in grapevine is associated with chloride (Cl−) exclusion from shoots; the rate-limiting step being the passage of Cl− between the root symplast and xylem apoplast. Despite an understanding of the physiological mechanism of Cl− exclusion in grapevine, the molecular identity of membrane proteins that control this process have remained elusive. To elucidate candidate genes likely to control Cl− exclusion, we compared the root transcriptomes of three Vitis spp. with contrasting shoot Cl− exclusion capacities using a custom microarray. Results When challenged with 50 mM Cl−, transcriptional changes of genotypes 140 Ruggeri (shoot Cl− excluding rootstock), K51-40 (shoot Cl− including rootstock) and Cabernet Sauvignon (intermediate shoot Cl− excluder) differed. The magnitude of salt-induced transcriptional changes in roots correlated with the amount of Cl− accumulated in shoots. Abiotic-stress responsive transcripts (e.g. heat shock proteins) were induced in 140 Ruggeri, respiratory transcripts were repressed in Cabernet Sauvignon, and the expression of hypersensitive response and ROS scavenging transcripts was altered in K51-40. Despite these differences, no obvious Cl− transporters were identified. However, under control conditions where differences in shoot Cl− exclusion between rootstocks were still significant, genes encoding putative ion channels SLAH3, ALMT1 and putative kinases SnRK2.6 and CPKs were differentially expressed between rootstocks, as were members of the NRT1 (NAXT1 and NRT1.4), and CLC families. Conclusions These results suggest that transcriptional events contributing to the Cl− exclusion mechanism in grapevine are not stress-inducible, but constitutively different between contrasting varieties. We have identified individual genes from large families known to have members with roles in anion transport in other plants, as likely candidates for controlling anion homeostasis and Cl− exclusion in Vitis species. We propose these genes as priority candidates for functional characterisation to determine their role in chloride transport in grapevine and other plants. Electronic supplementary material The online version of this article (doi:10.1186/s12870-014-0273-8) contains supplementary material, which is available to authorized users.

Plant cation-chloride cotransporters (CCCs) have been implicated in conferring salt tolerance. They are predicted to improve shoot salt exclusion by directly catalyzing the retrieval of sodium (Na(+)) and chloride (Cl(-)) ions from the root xylem. We investigated whether grapevine (Vitis vinifera [Vvi]) CCC has a role in salt tolerance by cloning and functionally characterizing the gene from the cultivar Cabernet Sauvignon. Amino acid sequence analysis revealed that VviCCC shares a high degree of similarity with other plant CCCs. A VviCCC-yellow fluorescent protein translational fusion protein localized to the Golgi and the trans-Golgi network and not the plasma membrane when expressed transiently in tobacco (Nicotiana benthamiana) leaves and Arabidopsis (Arabidopsis thaliana) mesophyll protoplasts. AtCCC-green fluorescent protein from Arabidopsis also localized to the Golgi and the trans-Golgi network. In Xenopus laevis oocytes, VviCCC targeted to the plasma membrane, where it catalyzed bumetanide-sensitive (36)Cl(-), (22)Na(+), and (86)Rb(+) uptake, suggesting that VviCCC (like AtCCC) belongs to the Na(+)-K(+)-2Cl(-) cotransporter class of CCCs. Expression of VviCCC in an Arabidopsis ccc knockout mutant abolished the mutant's stunted growth phenotypes and reduced shoot Cl(-) and Na(+) content to wild-type levels after growing plants in 50 mm NaCl. In grapevine roots, VviCCC transcript abundance was not regulated by Cl(-) treatment and was present at similar levels in both the root stele and cortex of three Vitis spp. genotypes that exhibit differential shoot salt exclusion. Our findings indicate that CCC function is conserved between grapevine and Arabidopsis, but neither protein is likely to directly mediate ion transfer with the xylem or have a direct role in salt tolerance.