Abstract
BackgroundSEVEN IN ABSENTIA (SINA) is a RING domain-containing ubiquitin ligase involved in Drosophila eye formation. SINA-like proteins in plants are involved in several signaling pathways. Of the 18 SINA-like proteins identified in Arabidopsis, SEVEN IN ABSENTIA 2 (SINA2) lacks a canonical RING domain and is thought to lack ubiquitin ligase activity.ResultsOur results show that SINA2 has E3 ligase activity in vitro, raising the possibility that a modified B-box domain may compensate for its lack of a RING domain. SINA2 physically interacts with the nuclear protein CYCLIN-DEPENDENT KINASE G1 (CDKG1), which acts as a positive regulator of plant responses to abiotic stress. CDKG1 is expressed in multiple tissues and its expression increased in response to abscisic acid (ABA) and osmotic stress. Transgenic Arabidopsis plants that ectopically express CDKG1 exhibit increased tolerance to ABA and osmotic stress treatments during seed germination and cotyledon development, while the loss-of-function cdkg1 mutant plants show reduced tolerance to ABA and osmotic stress treatments. Moreover, CDKG1-dependent phosphorylation of SINA2 positively affects its E3 ubiquitin ligase activity.ConclusionsBased on these results, we propose that CDKG1 modulates SINA2 ubiquitin ligase activity to regulate its effect on plant responses to ABA and osmotic stress.
Highlights
SEVEN IN ABSENTIA (SINA) is a Really Interesting New Gene (RING) domain-containing ubiquitin ligase involved in Drosophila eye formation
Our results indicate that up-regulation of the ubiquitin ligase activity of SEVEN IN ABSENTIA 2 (SINA2) by CYCLINDEPENDENT KINASE G1 (CDKG1)-dependent phosphorylation, could lead to altered stress responses in Arabidopsis
Since our results indicate that CDKG1 can affect SINA2 ubiquitin ligase activity (Fig. 7b), it seems likely that the effect of CDKG1 on abscisic acid (ABA) signaling is indirect
Summary
SEVEN IN ABSENTIA (SINA) is a RING domain-containing ubiquitin ligase involved in Drosophila eye formation. Of the 18 SINA-like proteins identified in Arabidopsis, SEVEN IN ABSENTIA 2 (SINA2) lacks a canonical RING domain and is thought to lack ubiquitin ligase activity. Plants are sessile and are unable to avoid stressful environmental conditions that often limit their growth and development. To survive these stresses, plants have evolved complex biochemical and physiological strategies that are controlled by a network of signaling events. More than 1400 genes that encode putative E3 ubiquitin ligases have been identified in the Arabidopsis genome [45]. The single-subunit enzymes include RING, U-box, and HECT domain-containing enzymes, while multiple-subunit CULLIN-based E3 ligase complexes include the Skp1-CULLIN1-F-box complex, CUL3-BTB and CUL4-DDB1 [37]
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