Can a Genetic Correlation with Seed Mass Constrain Adaptive Evolution of Seedling Desiccation Tolerance in Wild Barley?

Abstract

Very young seedlings of wild barley Hordeum spontaneum have the ability to survive extended periods of severe drought. This desiccation tolerance is considered an adaptation to the rain-limited and unpredictable habitats that the species occupies. Genetic variation has been observed for this trait, but the limited evidence to date does not consistently show that genotypes from more xeric populations have better desiccation tolerance. As large seed endosperm volume may buffer the desiccating seedling from drought stress, we explored the hypothesis that tolerance to temporary but severe drought is affected by seed mass. We crossed a big-seeded with a small-seeded H. spontaneum genotype and measured seed mass and seedling survival rates after 6-d desiccation in 140 F 4 progeny families. A positive correlation was observed between family mean scores of the two traits. At the genetic level, this indicated that at least some genes underlying variation in the two traits overlapped (or show close chromosomal linkage), which is inevitable if seed mass causally affects desiccation tolerance. Quantitative Trait Loci (QTL) analysis, which can identify chromosome regions responsible for trait variation by exploring associations between trait expression and genetic markers dispersed over the genome, did not confirm this hypothesis of shared genetic control. Despite the lack of QTL evidence, the observed genetic association between seed mass and desiccation tolerance indicates that the two traits are not fully independent, implying that selection targeting one trait will cause a correlated response in the other. We discuss this finding in the context of adaptive differentiation of H. spontaneum populations, which is thought to involve selection of increasingly smaller seeds along a gradient of decreasing predictability and amount of annual precipitation.

The Association Among Gene Expression Responses to Nine Abiotic Stress Treatments in Arabidopsis thaliana

“…A primary challenge, however, may reside in manipulating the expression of genes underlying multiple-stress tolerance without associated costs affecting plant fitness components, particularly if such genes are involved in central metabolic processes (Vinocur and Altman 2005). This challenge has been foreshadowed by decades of artificial selection experiments, in which diminished growth and productivity have often been found to result as a correlated response to selection for increased stress tolerance Hoffmann and Parsons 1989a;Verhoeven et al 2004;Sinebo 2005; but see Araus et al 2003). Similar growth and productivity costs have more recently been found in strains bioengineered for increased tolerance to adverse conditions (e.g., Kasuga et al 1999;Ito et al 2006) and have been an obstacle toward successful bioengineering of stress tolerance in plants (Vinocur and Altman 2005).…”

Evolution of plant resistance and tolerance to frost damage

“…Direct and indirect selection on seed mass (Stanton 1984; Mazer 1987; Gomez 2004; Verhoeven et al. 2004) and germination time (Gonzalez‐Astorga & Nunez‐Farfan 2000; Donohue 2002; Griffith et al.…”

“…2004) have been shown to be of evolutionary importance in other studies. For example, selection for larger seeds may lead to increased competitive ability and resistance to abiotic stress, but may also result in higher levels of seed predation (Gomez 2004; Verhoeven et al. 2004).…”

Germination of cotton cultivar seeds under water stress induced by polyethyleneglycol-6000

“…The same approach was applied for water restriction tests, using a 4 × 6 factorial scheme (cultivars × water potentials). The variables of the water restriction experiment were submitted to both deviance analysis and logistic regression analysis (Andersson et al, 2001;Verhoeven et al, 2004) the data in percentage were estimated by using the formula: p=[exp(n ij )/1+exp(n ij )] (Paula, 2001).…”