Abstract
Drought is one of the most adverse abiotic factors limiting growth and productivity of crops. Among them is barley, ranked fourth cereal worldwide in terms of harvested acreage and production. Plants have evolved various mechanisms to cope with water deficit at different biological levels, but there is an enormous challenge to decipher genes responsible for particular complex phenotypic traits, in order to develop drought tolerant crops. This work presents a comprehensive approach for elucidation of molecular mechanisms of drought tolerance in barley at the seedling stage of development. The study includes mapping of QTLs for physiological and biochemical traits associated with drought tolerance on a high-density function map, projection of QTL confidence intervals on barley physical map, and the retrievement of positional candidate genes (CGs), followed by their prioritization based on Gene Ontology (GO) enrichment analysis. A total of 64 QTLs for 25 physiological and biochemical traits that describe plant water status, photosynthetic efficiency, osmoprotectant and hormone content, as well as antioxidant activity, were positioned on a consensus map, constructed using RIL populations developed from the crosses between European and Syrian genotypes. The map contained a total of 875 SNP, SSR and CGs, spanning 941.86 cM with resolution of 1.1 cM. For the first time, QTLs for ethylene, glucose, sucrose, maltose, raffinose, α-tocopherol, γ-tocotrienol content, and catalase activity, have been mapped in barley. Based on overlapping confidence intervals of QTLs, 11 hotspots were identified that enclosed more than 60% of mapped QTLs. Genetic and physical map integration allowed the identification of 1,101 positional CGs within the confidence intervals of drought response-specific QTLs. Prioritization resulted in the designation of 143 CGs, among them were genes encoding antioxidants, carboxylic acid biosynthesis enzymes, heat shock proteins, small auxin up-regulated RNAs, nitric oxide synthase, ATP sulfurylases, and proteins involved in regulation of flowering time. This global approach may be proposed for identification of new CGs that underlies QTLs responsible for complex traits.
Highlights
Drought is one of the most devastating abiotic stresses which limits strongly crops growth and productivity
This study present a first comprehensive approach for elucidation of genetic basis of physiological mechanisms of drought response/tolerance in barley based on the identification of the positional candidate gene (CG) assembly within the QTL confidence intervals, followed by the exploration of their putative functions related to drought tolerance
Descriptive statistics for physiological/biochemical traits evaluated in the MCam recombinant inbred lines (RIL) population and parental genotypes is shown in Supplementary Material S3
Summary
Drought is one of the most devastating abiotic stresses which limits strongly crops growth and productivity. It varies in occurrence, duration and severity, and from location to location, and in the same location from year to year. Four major drought resistance mechanisms have been described and their indicators dissected: drought escape manifested by a short life cycle, photoperiod sensitivity and plasticity of development; drought avoidance through reduced water loss or increased water uptake; drought tolerance through osmotic adjustment and antioxidant capacity; and drought recovery related to capability to resume the growth after a complete loss of turgor pressure and leaf dehydration (Bray, 2007; Farooq et al, 2009; Chen et al, 2010; Fang and Xiong, 2015). Much slower progress has been made in understanding genetic basis of drought resistance and in developing more tolerant genotypes, owing to the genetic complexity of this trait and its quantitative inheritance with hundreds of genes of small, often epistatic and/or pleiotropic effects and low heritability (Tuberosa and Salvi, 2007; Cattivelli et al, 2011; Fan et al, 2015)
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