Poster: Membrane transport

Abs # 182: Calcium ATPase AtECA3 shows tissue-specific expression and supports root and pollen tube growth

Presenter:	Li, Xiyan , xyli@wam.umd.edu
Authors	Li, Xiyan  (A)   Harper, Jeffrey F. (B)   Romanowsky, Shawn  (B)   Sze, Heven  (A)
Affiliations:	(A): Department of Cell Biology and Molecular Genetics, University of Maryland (B): Department of Cell Biology, Plant Division, The Scripps Research Institute

In plant cells, several Ca-ATPase homologues are proposed to maintain submicromolar [Ca²⁺]_cyt and to load mM [Ca] into endomembrane compartments, though the specific roles of many ACA and ECA gene products from Arabidopsis are unknown. AtECA1, an ER-bound Ca/Mn pump, supported plant growth and conferred tolerance to Mn²⁺ stress (Wu et al. 2002, Plant Physiol 130:128). We are now investigating the biological roles of 3 other AtECA. AtECA3 (At1g10130) is strikingly different, as it shares higher identity (54%) with human ER/SER Ca₂₊ pumps than with three other AtECA (47%). AtECA3 expression in tissues as monitored by promoter::Gus analyses was extremely low compared with ECA1, ECA2 or ECA4. Expression of ECA3 was detected only in vascular tissues of root, young cotyledons and leaves. Three alleles of homozygous T-DNA insertional mutants (eca3-1, 3-4, and 3-5) were screened. Root growth in mutant eca3-1 and eca3-4 was reduced ~35% compared with wild-type on Johnson's media without Ca²⁺ supplement. Moreover, elongation of pollen tube in vitro was decreased significantly in all mutants when external Ca²⁺ was 10 mM. These results suggested that divalent cation loading into endomembrane compartments by ECA3 is important for rapid growth of root and pollen tube. The reduced root growth of eca3 mutants is perplexing considering ECA3 expression is low and limited to vascular tissues. ABA and GA-responsive cis-acting elements were found in ECA3, so we are testing hormonal responses of eca3 mutants. (Supported by DOE grant to HS)