Stress-induced DREB1A gene changes heliotropism and reduces drought stress in soybean plants under greenhouse conditions

The drought stress is one of the most severe environmental constraints for plant and food production. Development of cultivars for suitable drought environments can offer sustainable solutions. In order to avoid direct sunlight under drought conditions, some species show complex daily heliotropic adjustments of leaf angles that can reduce transpiration losses by diminishing the light interception (paraheliotropism). The diaheliotropism (solar tracking) is an opposite process that can increase diurnal carbon gain in sparse canopies and reduce carbon gain in dense canopies. A soybean cultivar BR 16 was genetically engineered producing the isoline P58 with intention to ectopically over express AtDREB1A, a transcription factor known to be involved in a biotic stress response. It was hypostatized that P58 will show better tolerance to drought stress compared to parental cultivar BR 16. The aim of the study was to follow the central and lateral leaflet movements in vegetative stages V7-V10 and to integrate heliotropic changes of BR 16 and P58 into an estimation of daily plant photosynthesis using 3D modelling. Soybean plants were grown in greenhouse, under optimized water supply and drought stress controlled by gravimetric humidity in pots. The plants were codified and reconstructed under the VPlants methodology. Leaflet movements and leaf gas exchange were measured in V7-V10 stages on leaflets of upper leaves by hourly-performed photo-shots and reproduced in 3D reconstructions. Under non-limited conditions, the BR 16 showed some diaheliotropic movements of the central and lateral leaflets, in the morning and early afternoon hours, while the central leaflet in P58 showed long lasting diaheliotropic movements in the morning and early afternoon with lateral leaflets constantly positioned parallel to solar rays. Under the drought stress, BR 16 responded by prevalent paraheliotropic movements of the central and lateral leaflets, while the central leaflets in P58 followed the paraheliotropic pattern, and the lateral ones showed diaheliotropic movements in the morning, early afternoon and late afternoon compensating the predominant central leaflet paraheliotropism. The mean leaf photosynthesis per plant in water-stressed P58 was maintained in the same level as in well-watered plants during the late morning hours. Results suggest that DREB1A could be involved in various responses to drought stress, from alleviating its impacts through the increasing of diaheliotropic movement frequency of lateral leaflets, to maintaining the same level of assimilation in late morning hours on plant scale.