Comparative Physiological and Transcriptome Profiling of Grapevine Rootstocks Identified Their Physiological Adaptations and Gene Regulation Networks behind Drought Tolerance

Since the roots of grapevine rootstocks have a direct contact with drying soil and has an important role in abiotic stimuli, any plasticity on the architecture of the rootstocks would enable grapevine varieties to a better respond to drought stress. However, genomics evidences behind the physiological responses of rootstocks under prolonged drought stress are poorly documented in the literature. In the current study, eight widely used hybrid grapevine rootstocks in viticulture were firstly grafted with sultana seedless and subjected to drought stress to test their physiological and biochemical responses. The results of experiment indicated that the roots of V.rupestris X V.berlandieri (110 R, 1103P, 140 Ru) rootstocks possessed much higher water content as well as non-structural carbohydrate and nitrogen concentrations compared to V.riparia X V.berlandieri (SO4, 5BB, 420A, 8B) and V.vinifera X V.berlandieri (41B) hybrids under drought. V.rupestris X V.berlandieri hybrids were also performed much higher root elongation performance under drought compared to other rootstock hybrids. Three rootstock varieties (110R, 5BB and 41B) having different pedigrees and root architectural responses to drought were also investigated at transcriptome level to find out gene regulation network behind differential physiological responses to drought. Transcriptome analysis revealed 2795, 1196 and 1612 differentially expressed transcripts for the roots of 110R, 5BB and 41B, respectively. The highest expression increases in 110R compared to other rootstocks were recorded for the transcripts functional in carbohydrate (SWEET14, CWINV) and nitrate/peptide (NRT1/ PTR FAMILY) transportation as well as osmoregulation (dehydrins, osmotins, LEAs and proline-glycine rich proteins) during drought. Higher induction of these genes in the roots of tolerant 110R genotype indicated importance of efficient uptake of carbohydrate and nitrogen source released from canopy under drought and preservation of water with osmotic regulation on the root elongation and drought tolerance of grapevines. Expression increases in several other pathogenesis related proteins, regulation of cell wall modification enzymes and activity of several secondary metabolites have been also associated to altered root architecture and drought tolerance in the grapevine rootstocks for the first time with the current study. Total RNA used in microarray experiment was isolated from the roots of grafted 110R, 5BB and 41B rootstocks. Total RNA used in the microarray experiment was isolated from the roots of plants grown under well watered and drought treated conditions. RNA isolation was made according to Lithium chloride precipitation method described in Chang et al. (1993). Roots of two replications were used in RNA isolation (biological replicates) for the plants and each isolated RNAs loaded onto one Affymetrix vitis Geneome arrays (technical replicates). Totally, 12 GeneChips (three different root tissue × 2 different water availibility × 2 biological replicates) were used for transcriptional analysis.