The relationship between root hydraulics and scion vigour across Vitis rootstocks: what role do root aquaporins play?
ABSTRACT: Vitis vinifera scions are commonly grafted onto rootstocks of other grape species to influence scion vigour and provide resistance to soil-borne pests and abiotic stress; however, the mechanisms by which rootstocks affect scion physiology remain unknown. This study characterized the hydraulic physiology of Vitis rootstocks that vary in vigour classification by investigating aquaporin (VvPIP) gene expression, fine-root hydraulic conductivity (Lp(r)), % aquaporin contribution to Lp(r), scion transpiration, and the size of root systems. Expression of several VvPIP genes was consistently greater in higher-vigour rootstocks under favourable growing conditions in a variety of media and in root tips compared to mature fine roots. Similar to VvPIP expression patterns, fine-root Lp(r) and % aquaporin contribution to Lp(r) determined under both osmotic (Lp(r)(Osm)) and hydrostatic (Lp(r)(Hyd)) pressure gradients were consistently greater in high-vigour rootstocks. Interestingly, the % aquaporin contribution was nearly identical for Lp(r)(Osm) and Lp(r)(Hyd) even though a hydrostatic gradient would induce a predominant flow across the apoplastic pathway. In common scion greenhouse experiments, leaf area-specific transpiration (E) and total leaf area increased with rootstock vigour and were positively correlated with fine-root Lp(r). These results suggest that increased canopy water demands for scion grafted onto high-vigour rootstocks are matched by adjustments in root-system hydraulic conductivity through the combination of fine-root Lp(r) and increased root surface area.
Project description:Water deficits are known to alter fine root structure and function, but little is known about how these responses contribute to differences in drought resistance across grapevine rootstocks. The ways in which water deficit affects root anatomical and physiological characteristics were studied in two grapevine rootstocks considered as low-medium (101-14Mgt) and highly (110R) drought resistant. Rootstocks were grown under prolonged and repeated drying cycles or frequent watering ('dry' and 'wet' treatments, respectively), and the following parameters were evaluated: root osmotic and hydrostatic hydraulic conductivity (Lp os and Lp hyd, respectively), suberization, steady-state root pressure (P rs), sap exudation rates, sap osmotic potential, and exosmotic relaxation curves. For both rootstocks, the 'dry' treatment reduced fine root Lp, elicited earlier root suberization and higher sap osmotic potential, and generated greater P rs after rewatering, but the rootstocks responded differently under these conditions. Lp os, Lp hyd, and sap exudation rates were significantly higher in 110R than in 101-14Mgt, regardless of moisture treatment. Under 'dry' conditions, 110R maintained a similar Lp os and decreased the Lp hyd by 36% compared with 'wet' conditions, while both parameters were decreased by at least 50% for 101-14Mgt under 'dry' conditions. Interestingly, build-up of P rs in 110R was 34% lower on average than in 101-14Mgt, suggesting differences in the development of suberized apoplastic barriers between the rootstocks as visualized by analysis of suberization from fluorescence microscopy. Consistent with this pattern, 110R exhibited the greatest exosmotic Lp os (i.e. Lp os of water flowing from roots to the soil) as determined from relaxation curves under wet conditions, where backflow may have limited its capacity to generate positive xylem pressure. The traits studied here can be used in combination to provide new insights needed for screening drought resistance across grapevine rootstocks.
Project description:Environments with short growing seasons and variable climates can have soil temperatures that are suboptimal for chilling-sensitive crops. These conditions can adversely affect root growth and physiological performance thus impairing water and nutrient uptake. Four greenhouse trials and a field study were conducted to investigate if rootstocks can enhance tomato performance under suboptimal soil temperatures (SST). In a controlled greenhouse environment, we exposed four commercial rootstocks (Estamino, Maxifort, RST-04-106-T, and Supernatural) grafted with a common scion (cv. BHN-589) to optimal (mean: 24°C) and SST (mean: 13.5°C) and compared their performance with the non-grafted BHN-589 cultivar. Several root and shoot physiological traits were evaluated: root hydraulic conductivity and conductance, root anatomy, leaf gas exchange, leaf ?<sup>13</sup>C, shoot C and N, and biomass. Under field conditions, the same five phenotypes were evaluated for canopy growth, normalized difference vegetation index (NDVI), leaf nutrients, biomass, and yield. Under SST, root hydraulic conductivity (<i>Lp</i>) and conductance (<i>K</i> <sub>R</sub>), stomatal conductance (<i>g</i> <sub>s</sub>), and plant biomass decreased. Hydrostatic <i>Lp</i> decreased more than osmotic <i>Lp</i> (<i>Lp</i> <sup>?</sup> <sub>hyd</sub>: 39-65%; <i>Lp</i> <sup>?</sup> <sub>os</sub>: 14-40%) and some of the reduced conductivity was explained by the increased cortex area of primary roots observed under SST (67-140%). Under optimal soil temperatures, all rootstocks conferred higher <i>g</i> <sub>s</sub> than the non-grafted cultivar, but only two rootstocks maintained higher <i>g</i> <sub>s</sub> under SST. All phenotypes showed greater reductions in shoot biomass than root biomass resulting in greater (?20%) root-to-shoot ratios. In the field, most grafted phenotypes increased early canopy cover, NDVI, shoot biomass, and fruit yield. Greenhouse results showed that <i>Lp</i> <sup>?</sup> <sub>os</sub> may be less affected by SST than <i>Lp</i> <sup>?</sup> <sub>hyd</sub> and that reductions in <i>Lp</i> may be offset by enhanced root-to-shoot ratios. We show that some commercial rootstocks possess traits that maintained better rates of stomatal conductance and shoot N content, which can contribute toward better plant establishment and improved performance under SST.
Project description:BACKGROUND:Grafting is widely used in horticulture and rootstocks are known to modify scion growth and adaptation to soil conditions. However, the role of scion genotype in regulating rootstock development and functioning has remained largely unexplored. In this study, reciprocal grafts of two grapevine genotypes were produced as well as the corresponding homo-graft controls. These plants were subjected to a low phosphate (LP) treatment and transcriptome profiling by RNA sequencing was done on root samples collected 27?h after the onset of the LP treatment. RESULTS:A set of transcripts responsive to the LP treatment in all scion/rootstock combinations was identified. Gene expression patterns associated with genetic variation in response to LP were identified by comparing the response of the two homo-grafts. In addition, the scion was shown to modify root transcriptome responses to LP in a rootstock dependent manner. A weighted gene co-expression network analysis identified modules of correlated genes; the analysis of the association of these modules with the phosphate treatment, and the scion and rootstock genotype identified potential hub genes. CONCLUSIONS:This study provides insights into the response of grafted grapevine to phosphate supply and identifies potential shoot-to-root signals that could vary between different grapevine genotypes.
Project description:In horticulture, grafting is a popular technique used to combine positive features of two different plants, obtained by joining a scion (generally the part above the ground) onto a rootstock (constituted by the stem and roots). Despite its wide-use, the biological mechanisms driving rootstock-induced alterations of the scion phenotype are not fully understood. Given that epigenetics is an important component of distance signalling in plants, we investigated the genome wide changes in the DNA methylation induced in eggplants grafted onto two interspecific rootstocks commercially used to induce scion vigour, compared to self-grafted plants. We found that vigour was associated to a specific change in scion gene expression and a genome wide hypo-methylation in CHH context. Interestingly, this hypomethylation correlated with downregulation of younger and potentially more active LTR retrotransposons. Our data indicate that graft-induced epigenetics modifications are associated to both physiological and molecular phenotypes in plants, and suggest that rootstocks can induce vigour by reducing DNA methylation in the scion genome, similarly to what observed in some heterotic hybrids. Overall design: Examination of DNA methylation of 2 wild type Solanum melongena plants, and two replicates of S. melongena scions grafted on S. melongena (self graft), Solanum torvum and Solanum lycopersicum (var. Emperador).
Project description:In horticulture, grafting is a popular technique used to combine positive features of two different plants, obtained by joining a scion (generally the part above the ground) onto a rootstock (constituted by the stem and roots). Despite its wide-use, the biological mechanisms driving rootstock-induced alterations of the scion phenotype are not fully understood. Given that epigenetics is an important component of distance signalling in plants, we investigated the genome wide changes in the DNA methylation induced in eggplants grafted onto two interspecific rootstocks commercially used to induce scion vigour, compared to self-grafted plants. We found that vigour was associated to a specific change in scion gene expression and a genome wide hypo-methylation in CHH context. Interestingly, this hypomethylation correlated with downregulation of younger and potentially more active LTR retrotransposons. Our data indicate that graft-induced epigenetics modifications are associated to both physiological and molecular phenotypes in plants, and suggest that rootstocks can induce vigour by reducing DNA methylation in the scion genome, similarly to what observed in some heterotic hybrids. Overall design: Transcriptional profile of 2 wild type Solanum melongena plants, and two replicates of S. melongena scions grafted on S. melongena (self graft), Solanum torvum and Solanum lycopersicum (var. Emperador).
Project description:The fact that silicon application alleviates water deficit stress has been widely reported, but the underlying mechanism remains unclear. Here the effects of silicon on water uptake and transport of sorghum seedlings (Sorghum bicolor L.) growing under polyethylene glycol-simulated osmotic stress in hydroponic culture and water deficit stress in sand culture were investigated. Osmotic stress dramatically decreased dry weight, photosynthetic rate, transpiration rate, stomatal conductance, and leaf water content, but silicon application reduced these stress-induced decreases. Although silicon application had no effect on stem water transport capacity, whole-plant hydraulic conductance (Kplant) and root hydraulic conductance (Lp) were higher in silicon-treated seedlings than in those without silicon treatment under osmotic stress. Furthermore, the extent of changes in transpiration rate was similar to the changes in Kplant and Lp. The contribution of aquaporin to Lp was characterized using the aquaporin inhibitor mercury. Under osmotic stress, the exogenous application of HgCl2 decreased the transpiration rates of seedlings with and without silicon to the same level; after recovery induced by dithiothreitol (DTT), however, the transpiration rate was higher in silicon-treated seedlings than in untreated seedlings. In addition, transcription levels of several root aquaporin genes were increased by silicon application under osmotic stress. These results indicate that the silicon-induced up-regulation of aquaporin, which was thought to increase Lp, was involved in improving root water uptake under osmotic stress. This study also suggests that silicon plays a modulating role in improving plant resistance to osmotic stress in addition to its role as a mere physical barrier.
Project description:The apple dwarfing rootstock 'Malling9' ('M9') has been used worldwide both to reduce scion vigour and as a genetic source for breeding new rootstocks. Progeny of 'M9' segregate for rootstock-induced dwarfing of the scion, indicating that this trait is controlled by one or more genetic factors. A quantitative trait locus (QTL) analysis of a rootstock population derived from the cross between 'M9' × 'Robusta5' (non-dwarfing) and grafted with 'Braeburn' scions identified a major QTL (Dw1) on linkage group (LG) 5, which exhibits a significant influence on dwarfing of the scion. A smaller-effect QTL affecting dwarfing (Dw2) was identified on LG11, and four minor-effect QTLs were found on LG6, LG9, LG10 and LG12. Phenotypic analysis indicates that the combination of Dw1 and Dw2 has the strongest influence on rootstock-induced dwarfing, and that Dw1 has a stronger effect than Dw2. Genetic markers linked to Dw1 and Dw2 were screened over 41 rootstock accessions that confer a range of effects on scion growth. The majority of the dwarfing and semi-dwarfing rootstock accessions screened carried marker alleles linked to Dw1 and Dw2. This suggests that most apple dwarfing rootstocks have been derived from the same genetic source.
Project description:BACKGROUND:Although it is known that resistant rootstocks facilitate management of fire blight disease, incited by Erwinia amylovora, the role of rootstock root traits in providing systemic defense against E. amylovora is unclear. In this study, the hypothesis that rootstocks of higher root vigor provide higher tolerance to fire blight infection in apples is tested. Several apple scion genotypes grafted onto a single rootstock genotype and non-grafted 'M.7' rootstocks of varying root vigor are used to assess phenotypic and molecular relationships between root traits of rootstocks and fire blight susceptibility of apple scion cultivars. RESULTS:It is observed that different root traits display significant (p?<?0.05) negative correlations with fire blight susceptibility. In fact, root surface area partially dictates differential levels of fire blight susceptibility of 'M.7' rootstocks. Furthermore, contrasting changes in gene expression patterns of diverse molecular pathways accompany observed differences in levels of root-driven fire blight susceptibility. It is noted that a singular co-expression gene network consisting of genes from defense, carbohydrate metabolism, protein kinase activity, oxidation-reduction, and stress response pathways modulates root-dependent fire blight susceptibility in apple. In particular, WRKY75 and UDP-glycotransferase are singled-out as hub genes deserving of further detailed analysis. CONCLUSIONS:It is proposed that low root mass may incite resource-limiting conditions to activate carbohydrate metabolic pathways, which reciprocally interact with plant immune system genes to elicit differential levels of fire blight susceptibility.
Project description:<h4>Background and aims</h4>Limited supply of mineral nutrients often reduces plant growth and transpirational water flow while increasing the ratio of water-absorbing root to water-losing shoot surface. This could potentially lead to an imbalance between water uptake (too much) and water loss (too little). The aim of the present study was to test whether, as a countermeasure, the hydraulic properties (hydraulic conductivity, Lp) of roots decrease at organ and cell level and whether any decreases in Lp are accompanied by decreases in the gene expression level of aquaporins (AQPs) or increases in apoplastic barriers to radial water movement.<h4>Methods</h4>Barley plants were grown hydroponically on complete nutrient solution, containing 2 mm K+ (100 %), or on low-K solution (0.05 mm K+; 2.5 %), and analysed when they were 15-18 d old. Transpiration, fresh weight, surface area, shoot water potential (?), K and Ca concentrations, root (exudation) and cortex cell Lp (cell pressure probe), root anatomy (cross-sections) and AQP gene expression (qPCR) were analysed.<h4>Key results</h4>The surface area ratio of root to shoot increased significantly in response to low K. This was accompanied by a small decrease in the rate of water loss per unit shoot surface area, but a large (~50 %) and significant decrease in Lp at root and cortex cell levels. Aquaporin gene expression in roots did not change significantly, due to some considerable batch-to-batch variation in expression response, though HvPIP2;5 expression decreased on average by almost 50 %. Apoplastic barriers in the endodermis did not increase in response to low K.<h4>Conclusions</h4>Barley plants that are exposed to low K adjust to an increased ratio of root (water uptake) to shoot (water loss) surface primarily through a decrease in root and cell Lp. Reduced gene expression of HvPIP2;5 may contribute to the decrease in Lp.
Project description:In many fruit species, including grapevine, grafting is used to improve scion productivity and quality and to adapt the plant to environmental conditions. However, the mechanisms underlying the rootstock control of scion development are still poorly understood. The ability of rootstocks to regulate nitrogen uptake and assimilation may contribute to this control. A split-root system was used to grow heterografted grapevines and to investigate the molecular responses to changes in nitrate availability of two rootstocks known to affect scion growth differently. Transcriptome profiling by RNA sequencing was performed on root samples collected 3 and 24 h after nitrogen supply. The results demonstrated a common response involving nitrogen-related genes, as well as a more pronounced transcriptomic reprogramming in the genotype conferring the lower scion growth. A weighted gene co-expression network analysis allowed the identification of co-regulated gene modules, suggesting a role for nitrate transporter 2 family genes and some transcription factors as main actors controlling this genotype-dependent response to heterogeneous nitrogen supply. The relationship between nitrate, ethylene, and strigolactone hormonal pathways was found to differ between the two genotypes. These findings indicated that the genotypes responded differently to heterogeneous nitrogen availability, and this may contribute to their contrasting effect on scion growth.