NUA and ESD4 negatively regulate ABA signaling during seed germination

The phytohormone abscisic acid(ABA)plays important roles in plant growth,development and adaptative responses to abiotic stresses.SNF1-related protein kinase 2s(SnRK2)are key components that activate the ABA core signaling pathway.NUCLEAR PORE ANCHOR(NUA)is a component of the nuclear pore complex(NPC)that involves in deSU-MOylation through physically interacting with the EARLY IN SHORT DAYS 4(ESD4)SUMO protease.However,it is not clear how NUA functions with SnRK2 and ESD4 to regulate ABA signaling.In our study,we found that nua loss-of-function mutants exhibited pleiotropic ABA-hypersensitive phenotype.We also found that ABA-responsive genes remarkably up-regulated in nua by exogenous ABA.The nua snrk2.2 snrk2.3 triple mutant and nua abi5 double mutant partially rescued the ABA-hypersensitive phenotype of nua,thereby suggesting that NUA is epistatic to SnRK2s.Additionally,we observed that esd4-3 mutant was also ABA-hypersensitive.NUA and ESD4 were further demonstrated to physically interact with SnRK2s and negatively regulate ABA signaling by reducing SnRK2s stability.Taken together,our findings uncover a new regulatory mechanism that can modulate ABA signaling.

NUCLEAR PORE ANCHOR and EARLY IN SHORT DAYS 4 negatively regulate abscisic acid signaling by inhibiting Snf1-related protein kinase2 activity and stability in Arabidopsis

Abscisic acid(ABA)is a key regulator of plant responses to abiotic stresses,such as drought.Abscisic acid receptors and coreceptors perceive ABA to activate Snf1-related protein kinase2 s(SnRK2s)that phosphorylate downstream effectors,thereby activating ABA signaling and the stress response.As stress responses come with fitness penalties for plants,it is crucial to tightly control SnRK2 kinase activity to restrict ABA signaling.However,how SnRK2 kinases are inactivated remains elusive.Here,we show that NUCLEAR PORE ANCHOR(NUA),a nuclear pore complex(NPC)component,negatively regulates ABA-mediated inhibition of seed germination and post-germination growth,and drought tolerance in Arabidopsis thaliana.The role of NUA in response to ABA depends on SnRK2.2 and SnRK2.3 for seed germination and on SnRK2.6 for drought.NUA does not directly inhibit the phosphorylation of these SnRK2s or affects their abundance.However,the NUA-interacting protein EARLY IN SHORT DAYS 4(ESD4),a SUMO protease,negatively regulates ABA signaling by directly interacting with and inhibiting SnRK2 phosphorylation and protein levels.More importantly,we demonstrated that SnRK2.6 can be SUMOylated in vitro,and ESD4 inhibits its SUMOylation.Taken together,we identified NUA and ESD4 as SnRK2 kinase inhibitors that block SnRK2 activity,and reveal a mechanism whereby NUA and ESD4 negatively regulate plant responses to ABA and drought stress possibly through SUMOylation-dependent regulation of SnRK2s.