Functional differences in transport properties of natural HKT1;1 variants influence shoot Na(+) exclusion in 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(+) ) 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.Sam W. Henderson, Jake D. Dunlevy, Yue Wu, Deidre H. Blackmore, Rob R. Walker, Everard J. Edwards, Matthew Gilliham, Amanda R. Walke

Shoot chloride exclusion and salt tolerance in grapevine is associated with differential ion transporter expression in roots

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.Sam W Henderson, Ute Baumann, Deidre H Blackmore, Amanda R Walker, Rob R Walker and Matthew Gilliha

Three-year field response of drip-irrigated grapevine (Vitis vinifera L., cv. Tempranillo) to soil salinity

24 Pag., 6 Tabl., 3 Fig. The definitive version is available at: http://www.springerlink.com/content/0032-079x/We evaluated the salinity tolerance of young Tempranillo grapevines over a three year’s period, and the related effects on growth to leaf Na and Cl concentrations. Soil salinity, rootstock growth and leaf Na and Cl concentrations were measured in a drip-irrigated saline field. Salinity tolerance was determined using the slope (percent growth decline per unit increase in soil salinity) of the upper-boundary line fitted to the maximum growth-salinity observations. Based on a slope of 17.1% for the 3 years, Tempranillo was shown to be more sensitive to salinity than other reported varieties (slopes between 9.3% and 13.2%). The salinity tolerance of Tempranillo decreased along the study period. Tempranillo excluded Cl and, in particular, Na from the leaves more efficiently than other grape rootstock-scion combinations. Tempranillo was classified as moderately sensitive to salinity, and decreases in growth with increases in salinity were attributed to the osmotic effect rather than to specific ion toxicities.This study was partially supported by the European Commission (INCO-CT-2005-015031) and by an INIA (Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Spain) doctoral fellowship given to V. Urdanoz.Peer reviewe