Abstract
The Arabidopsis genome comprises eighty genes encoding BTB (broad-complex, tramtrack, and bric-a-brac) family proteins that are characterized with the BTB domain and that potentially serve as substrate adaptors for cullin-based E3-ligases. In addition to the BTB domain, most BTB proteins also contain various other interaction motifs that probably act as target recognition elements. Here, we report three members of the BTB-A2 subfamily that distinctly only contain the BTB domain, BTB-A2.1, BTB-A2.2, and BTB-A2.3, that negatively regulates abscisic acid (ABA) signaling in Arabidopsis. BTB-A2.1, BTB-A2.2, and BTB-A2.3 encoded cytoplasm- and nucleus-localized proteins and displayed highly overlapping expression patterns in Arabidopsis tissues. Disruption of these three genes, but not single or double mutants, resulted in a decrease in ABA-induced inhibition of seed germination. Further analyses demonstrated the expression levels of these three genes were up-regulated by ABA, and their mutation increased ABA signalling. Importantly, protein-protein interaction assays showed that these three BTB-A2 proteins physically interacted with SnRK2.3. Moreover, biochemical and genetic assays indicated that BTB-A2.1, BTB-A2.2, and BTB-A2.3 decreased the stability of SnRK2.3 and attenuated the SnRK2.3 responsible for the ABA hypersensitive phenotype of seed germination. This report thus reveals that BTB-A2s serve as negative regulators for balancing the intensity of ABA signaling during seed germination.
Highlights
Seed germination is crucial for next-generation plant growth during the life cycle
The phylogenetic tree based on the query sequences agreed well with the evolutionary relationship among these species (Figure S1), suggesting BTB proteins are functionally important in eukaryotes
BTB-A2.2, or BTB-A2,3-GFP were all detected in the cytoplasmic areas and did not appear the areas occupied by chloroplasts or the central vacuole, the same distribution as the control GFP signals (Figure 1A), indicating that these three BTB-A2s proteins probably localized in the cytosol
Summary
Seed germination is crucial for next-generation plant growth during the life cycle. Seed germination is frequently a consequence of the competitive interaction between the growth potential of embryonic material and the limited mechanical force of its surrounding tissues, of which the process is elaborately regulated by internal and external signals [1,2,3,4]. Without ABA, there is a physical interaction between protein phosphatases 2C (PP2Cs) and sucrose non-fermenting-1-related protein kinases 2 (SnRK2s), which inhibits the phosphorylation activity of SnRK2s and turns ABA signalling off [7]. The released SnRK2s are activated and can phosphorylate the downstream proteins to turn on ABA signalling [7,11]. It is reported that AtSCFAtPP2-B11 regulates plants to response to ABA by degrading SnRK2.3 [16] These researchers demonstrated that several components that modify the modulators of ABA signalling may further reveal the molecular foundation of ABA signalling networks, allowing plants to adapt the environment to grow, develop, and reproduce. 2020, 21, 3153 this study has revealed a previously unrecognized mechanism of maintaining the appropriate ABA signalling level via SnRK2.3 in finely tuned seed germination Sci. 2020, 21, 3153 this study has revealed a previously unrecognized mechanism of maintaining the appropriate ABA signalling level via SnRK2.3 in finely tuned seed germination
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