Similar transcriptomic responses to early and late drought stresses produce divergent phenotypes in sunflower (Helianthus annuus L.)

Cultivated sunflower (Helianthus annuus L.) exhibits numerous phenotypic and transcriptomic responses to drought. However, the ways in which these responses vary with differences in drought timing and severity are insufficiently understood. We used phenotypic and transcriptomic data to evaluate the response of sunflower to drought scenarios of different timing and severity in a common garden experiment. Using a semi-automated outdoor high-throughput phenotyping platform, we grew six oilseed sunflower lines under control and drought conditions. Our results reveal that similar transcriptomic responses can have disparate phenotypic effects when triggered at different developmental time points. Leaf transcriptomic responses, however, share similarities despite timing and severity differences (e.g., 523 differentially expressed genes (DEGs) were shared across all treatments), though increased severity elicits greater differences in expression, particularly during vegetative growth. Across tr..., Six sunflower maintainer (B) lines bred for oil-rich seeds from the SAM population (HA124, HA370, HA412HO, HA850, HAR4, and SF193, also known as XRQ) were grown at the Heliaphen outdoor high-throughput phenotyping platform at INRAE Toulouse (France) in 2018. Seeds were planted on 17 April 2018 in 10 L pots of Terreau Proveen PAM 2 substrate. Plants were fertilized with 300 mL of Peter’s Professional 17-07-27 and 200 mL of Hortrilon per pot on 5 May, 25 May, and 13 June, and were provided Ortiva Top fungicide on 28 May and 15 June. Pots were maintained at specified soil moisture levels by measuring the pot weights daily and refilling them with water to return the pot weights to target levels. Soil around the plants was covered with a silicone cover to limit soil evaporation and was protected from rain using a cone-shaped polystyrene skirt. Drought treatment regimes were imposed by permitting pot weights to drop to specified levels for set periods of time.
Plants were grown under one of f...,