Nuclear accumulation of DELLA proteins induces transcriptional reprogramming and is well known to suppress the gibberellin (GA) pathway. While DELLAs can negatively regulate GA, increased GA levels can also signal DELLA degradation. GA is a growth-regulating hormone that is also involved in inhibiting the stress-signaling hormone ABA, but the mechanism behind this action is unclear. Nir et al. investigate the potential of DELLA proteins to connect these opposing hormone signaling pathways. The tomato genome encodes one DELLA gene, PROCERA (PRO). Semi dominate-negative pro mutants, in which DELLA activity is substantially diminished, exhibited decreased drought tolerance, increased stomatal pores, and increased transpiration rates. Conversely, Gain-of-function rgaΔ17 mutants, which express weak but constitutively active DELLA proteins, show the opposite phenotype: increased drought tolerance and decreased transpiration rates and stomatal pore size. Furthermore, DELLA activity enhanced ABA-induced stomatal closure and upregulated transcription of the ABA receptor PYR1. The authors concluded that DELLA, although not promoting ABA accumulation, does act in a GC-specific manner to enhance ABA-induced stomatal closure. DELLA likely acts upstream of ABA-induced ROS production and promotes ABA binding to PR/PYL/RCAR. These findings suggest that DELLAs are important for plant adaptation to drought stress. (Summary by Alecia Biel) Plant Cell. 10.1105/tpc.17.00542.
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