GA Signaling Increases Cytosolic Calcium

Gibberellins (GAs) regulate many aspects of plant development, including seed germination, stem elongation, flower induction, and anther development. DELLA proteins, of which there are 5 in Arabidopsis (Arabidopsis thaliana), play a central role in GA signaling. GA triggers DELLA degradation via the ubiquitin-proteasome pathway, thereby promoting plant growth. Some transcriptome analyses, however, have suggested that some GA-regulated genes are DELLA- independent. Another reported response of plant cells to GAs is an increase in [Ca²⁺]_cyt, although this increase occurs 1 h to several hours after GA application, too slow for Ca²⁺ to act as a secondary messenger of GA signaling. The mechanism by which GAs induce this increase in [Ca²⁺]_cyt, and whether this response is DELLA-related remains unknown. Okada et al. (10.1104/pp.17.01433) have reexamined the effects of GAs on [Ca²]⁺_cyt using the Ca²⁺ sensor protein aequorin in Arabidopsis (Arabidopsis thaliana). They report that [Ca²⁺]_cyt increases within a few minutes of GA treatment, even in transgenic plants expressing a mutated degradation-resistant version of a DELLA protein as well as in della pentuple mutant plants. In addition, it was also revealed that Ca²⁺ is not involved in DELLA degradation. These results suggest that the GA-induced increase in [Ca²⁺]_cyt occurs via a DELLA-independent pathway, providing important information on this aspect of the GA signaling network.