Abstract
In Mediterranean environments, water deficiency and heat during reproduction severely limit cereal crop production. Our research investigated the effects of single and combined pre-anthesis water-deficit stress and post-anthesis heat stress in ten Australian durum genotypes, providing a systematic evaluation of stress response at the molecular, physiological, grain quality and yield level. We studied leaf physiological traits at different reproductive stages, evaluated the grain yield and quality, and the associations among them. We profiled the expression dynamics of two durum microRNAs and their protein-coding targets (auxin response factors and heat shock proteins) involved in stress adaptation. Chlorophyll content, stomatal conductance and leaf relative water content were mostly reduced under stress, however, subject to the time-point and genotype. The influence of stress on grain traits (e.g., protein content) also varied considerably among the genotypes. Significant positive correlations between the physiological traits and the yield components could be used to develop screening strategies for stress improvement in breeding. Different expression patterns of stress-responsive microRNAs and their targets in the most stress-tolerant and most stress-sensitive genotype provided some insight into the complex defense molecular networks in durum. Overall, genotypic performance observed indicates that different stress-coping strategies are deployed by varieties under various stresses.
Highlights
Durum wheat (Triticum turgidum L. ssp. durum) is the only tetraploid wheat (2n = 4x = 28, genomes AABB) grown commercially worldwide, because of its unique grain characteristics and versatile end uses
Under water-deficit stress group (WS), the chlorophyll content was significantly decreased compared with control group (CG) at all five time-points for all ten genotypes (Fig. 1)
Under water-deficit plus heat stress group (WSHS), a significant decrease compared with CG was observed for all genotypes at all time-points
Summary
High temperatures (33–40 °C) for short periods of time (1–3 days) occurring periodically could be considered as heat shock while relatively mild heat stress (ranging from 20–32 °C) that lasts for a sustained period of time is considered as chronic heat stress[4,15,26,27] Both stress conditions are known to cause significant yield penalty and impact on grain quality but with varied effects. We have identified a water-deficit stress-responsive miRNA, miR396, which targets three genes that encode high-molecular weight heat shock proteins (HSP90)[24,38]. A recent study on two Italian durum cultivars with contrasting water-use efficiency has revealed cultivar-specific expression profiles of durum miRNAs (including miR160 and miR396) in response to heat shock and drought stress at the vegetative stage[42]. Analysis of the gene expression dynamics under single stress and stress combinations in parallel is important to gain further information on the possible synergistic interactions between the two stress types
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