The Function And Regulation Of Calcineurin And Calcium Channel CehA In Response To Salt Ions And Other Stresses In Aspergillus Nidulans

Calcium-mediated signaling mechanisms are widely employed in eukaryotes and are implicated in the regulation of diverse biological processes including gene expression,exocytosis,cytoskeletal,rearrangement,and cell morphology.Small changes in cytoplasmic Ca2+ levels can activate various Ca2+-sensing proteins,such as calmodulin and calcineurin,which then lead to the induction of various downstream signal transduction pathways.Although the high affinity Ca2+ channel(Cch1 and Mid1)and calcineurin have been investigated and evaluated in yeast and some of filamentous fungi,little is known about the internal relationship of calcium channel and calcineurin signaling cascade during the response to stress in Aspergillus nidulans.Furthermore,contribution of calcineurin catalytic subunit CnaA and regulatory subunit CnaB in response to varities of stresses in Aspergillus nidulans have not been well studied yet.Here,we found that ?cnaA/?cchA double mutants showed similar phenotypes to?cnaB/?cchA,both had more ploarity defects than that of single mutant in minimal medium.Moreover,adding extracellular salt stress(0.8 M NaCl and 0.6 M KC1)induced more severe growth defects in AcnaA or ?cnaB single mutants.In contrast,it is quite superising that the extracellular salt stress was able to significantly rescue the polarity defect of double mutants.Furthermore,extracellularly added NaCl plus calcium chelators EGTAcould improve the polarity growth of ?cnaA and ?cnaB single mutant indicating that cytoplasmic Ca2+ homeostasis may play a very important role in the polarity improvement of AcnaB/?cchA or ?cnaA/?cchA double mutants.These results suggest the absence of CchA could improve the polarity growth in CnaA and CnaB mutant during the response to salt stress,indicating that CchA may act as a reverse way with Calcineurin in the regulation of polarity growth in response to extracellular salt stress.And,we found that the gene expression of yvc(a calcium extrusion pump in vesicles)was down-regulated,and vcx(a calcium efflux pump in vesicles)was up-regulated,indicating that cytoplasmic Ca2+homeostasis may play a very important role in the polarity improvement of ?cnaB/?cchA or ?cnaA/?cchA double mutants.We also found that the overexpression of ena(a Na+channel)and hog(a osmotic stress response gene)induced by salt stress in ?cna?/AcchA double mutant might be the reason for salt stress tolerance.In additon,compared to the?cnaA/?cchA and ?cnaA/?cchA doule mutants,calcineurin mutant displayed less external cellular calcium tolerance and resulted in a phenotype with more swollen hyphal tips with a potentially disturbed calcium homeostasis,indicating that calcineurin mutant sensitivity to external Ca2+ could be rescued by deletion of CchA.Moreover,we also found when in responsed to cell wall stress,calcineurin mutant showed extremely sensitive to Congo Red and CFW,and Calcineurin and CchA double mutant still remaind highly sensitive to cell wall stress,suggesting CchA may not act as a reverse way with Calcineurin in the regulation of hyphae growth in response to cell wall stress.Taken together,our findings suggest that calcium channel-CchA may act as a reverse way with calcineurin in response to extracellular salt stress and external cellular calcium sensitive in addition to cell wall stress.And the calcineurin regulatory subunit CnaB play the same roles with catalytic subunit CnaA in response to varities of stresses in Aspergillus nidulans.