Abstract
Our previous study suggested that increased cytoplasmic calcium (Ca) signals may mediate aluminum (Al) toxicity in yeast (Saccharomyces cerevisiae). In this report, we found that a yeast mutant, pmc1, lacking the vacuolar calcium ion (Ca2+) pump Ca2+-ATPase (Pmc1p), was more sensitive to Al treatment than the wild-type strain. Overexpression of either PMC1 or an anti-apoptotic factor, such as Bcl-2, Ced-9 or PpBI-1, decreased cytoplasmic Ca2+ levels and rescued yeast from Al sensitivity in both the wild-type and pmc1 mutant. Moreover, pretreatment with the Ca2+ chelator BAPTA-AM sustained cytoplasmic Ca2+ at low levels in the presence of Al, effectively making the cells more tolerant to Al exposure. Quantitative RT-PCR revealed that the expression of calmodulin (CaM) and phospholipase C (PLC), which are in the Ca2+ signaling pathway, was down-regulated under Al stress. This effect was largely counteracted when cells overexpressed anti-apoptotic Ced-9 or were pretreated with BAPTA-AM. Taken together, our results suggest that the negative regulation of Al-induced cytoplasmic Ca signaling is a novel mechanism underlying internal resistance to Al toxicity.
Highlights
Aluminum (Al) toxicity has been implicated as a major cause of severe loss of crops grown in acidic soils
Consistent with Al sensitivity of the pmc1 mutant, these results suggest that cytosolic Ca2+ homeostasis and PMC1 activation are important for Al tolerance
We investigated the relevance of a vacuole-located Ca2+-ATPase PMC1 in modulating Al stress responses and the function of cytoplasmic Ca homeostasis on Al tolerance in yeast
Summary
Aluminum (Al) toxicity has been implicated as a major cause of severe loss of crops grown in acidic soils. Phosphoinositidespecific phospholipase C (PLC) is responsible for the production of two second-messenger molecules, containing an activator of protein kinase C diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3), which in turn releases Ca from internal stores [37,38] Al can induce both PCD and Ca burst in yeast, and antiapoptotic members can enhance Al tolerance coincident with decreased Ca signals [13]. Understanding the mechanisms through which cytoplasmic Ca2+ regulates Al stress will provide insights into the process of reducing Al toxicity in plants To this end, we investigated the functional roles of Pmc1p, the Ca2+ chelator BAPTA-AM and anti-apoptotic members in modulating cytosolic Ca2+ and facilitating Al tolerance
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