Abstract
BackgroundSalt 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.ResultsWhen 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.ConclusionsThese 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 materialThe online version of this article (doi:10.1186/s12870-014-0273-8) contains supplementary material, which is available to authorized users.
Highlights
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
140 Ruggeri accumulated significantly less petiole and laminae Cl− than K51-40, indicating that the Cl− exclusion mechanism may be active in low Cl− conditions (Figure 1B and C)
Validation of microarray data using real-time quantitative PCR To validate the microarray expression data and further quantify mRNA expression levels, we measured the expression of 12 genes by Quantitative real-time PCR (qRT-PCR) and compared the datasets
Summary
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. Despite a detailed understanding of the physiology of shoot Cl− accumulation in grapevine and other plants, the genes responsible for this process across the plant kingdom are not known [9]. This is in contrast to the control of long-distance Na+ transport in plants where numerous reports have targeted known genes in order to improve the salt tolerance of plants, cereals e.g. Due to extensive natural variation in the shoot Cl− exclusion capacity of Vitis spp
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