Water Deficit in Soybean Modifies Expression of Drought Responsive Genes Under Circadian Clock Control

Water deficit is one of the major abiotic factors limiting crop productivity, and yield losses are directly related with the intensity, duration and developmental stage when the stress occurs. In soybean, flower number and how water deficit alters flower number amount, flower establishment and flower durability directly affects yield components including number of pods, number of seeds, and seed weight. Temperature and length of the day are major factors controlling flowering in soybean. Recent studies in model plants have showed a tight connection between plants responses to abiotic stresses and the circadian clock. The circadian clock allows organisms to predict environmental cycles, such as day/night and seasons, and set plant metabolism accordingly, as well as to initiate processes like flowering under appropriate conditions. Using qPCR and RNA-Seq we have been examining how soybean circadian clock genes respond to increasing drought stress, as well as the impact of circadian regulation on soybean drought responsive genes. For crop plants such as soybean, little is known regarding how these key regulatory mechanisms interact and affect transcriptional activity. Many drought responsive soybean genes exhibit rhythmic expression.  Also, drought stress conditions induced marked changes in the expression of several soybean circadian clock-like genes. LCL1-, GmELF4-like, and several PRR-like genes had reduced expression in plants experiencing drought stress, while the same conditions produced changes in the phase of expression for GmTOC1-like, GmLUX-like and GmPRR7-like genes.  This study suggests that significant regulatory crosstalk exists between the soybean circadian clock and the signaling pathways involved in drought response.