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Reference: Li X, et al. (2008) A Distinct Endosomal Ca2+/Mn2+ Pump Affects Root Growth through the Secretory Process. Plant Physiol 147(4):1675-89

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Abstract


Ca(2+) is required for protein processing, sorting and secretion in eukaryotic cells, although the particular roles of transporters involved in the secretory system of plants are obscure. One Ca-ATPase from Arabidopsis thaliana, AtECA3, diverges from AtECA1, AtECA2 and AtECA4 in protein sequence; yet AtECA3 appears similar in transport activity to the ER-bound AtECA1. Expression of AtECA3 in a yeast mutant defective in its endogenous Ca(2+) pumps conferred ability to grow on Ca(2+)-depleted medium and tolerance to toxic levels of Mn(2+). A green fluorescent protein (GFP)-tagged AtECA3 was functionally competent and localized to intracellular membranes of yeast, suggesting that Ca(2+) and Mn(2+) loading into internal compartment(s) enhanced yeast proliferation. In mesophyll protoplasts, AtECA3-GFP associated with a subpopulation of endosome/prevacuolar compartments based on partial co-localization with Ara7 marker. Interestingly, three independent eca3 T-DNA disruption mutants showed severe reduction in root growth normally stimulated by 3 mM Ca(2+), indicating that AtECA3 function cannot be replaced by an ER-associated AtECA1. Furthermore, root growth of mutants is sensitive to 50 microM Mn(2+), indicating that AtECA3 is also important for the detoxification of excess Mn(2+). Curiously, Ateca3 mutant roots produced 65% more apoplastic protein than wild-type as monitored by peroxidase activity, suggesting the secretory process was altered. Together these results demonstrate that the role of AtECA3 is distinct from that of the more abundant ER AtECA1. AtECA3 supports Ca(2+)-stimulated root growth and the detoxification of high Mn(2+), possibly through activities mediated by post-Golgi compartments that coordinate membrane traffic and sorting of materials to the vacuole and the cell wall.

Reference Type
Journal Article
Authors
Li X, Chanroj S, Wu Z, Romanowsky SM, Harper JF, Sze H
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