|Zhao, Jian - BAYLOR COLLEGE MED|
|Cheng, Ning-Hui - BAYLOR COLLEGE MED|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 4, 2006
Publication Date: May 17, 2006
Citation: Zhao, J., Cheng, N-H., Hirschi, K.D. 2006. Arabidopsis CAX1 and CAX3 are involved in ABA and ethylene responses [abstract]. The 2nd Pan American Plant Membrane Biology Workshop, May 17-20, 2006, South Padre Island, Texas. P31, p. 92. Technical Abstract: Ca(2+) is a central second messenger involved in most of biological processes including hormonal and environmental plant responses. Plants regulate calcium levels through many mechanisms such as plasma membrane and endomembrane Ca(2+) channels, and endomembrane antiporters. Cation/H(+) exchangers (CAXs) in plants play important roles in regulating metal homeostasis. Arabidopsis CAXs were cloned by their ability to suppress the calcium sensitivity of yeast strains deficient in vacuolar Ca(2+) transport. However, the various roles of CAXs in plant cells are not fully understood. Both CAX1 and CAX3 are localized in the tonoplast of plant cells and were proposed to remove excessive cytosolic Ca(2+) into vacuole during plant responses. Genetic analysis of "CAX1" deletion plants suggests that CAX1 plays a role in auxin-mediated signaling. Here we report the involvement of "CAX1" and "CAX3" in ABA and ethylene responses during seed germination and seedling development. In comparison with wild type, both "CAX1" and "CAX3" mutant ("cax1-1, cax3-1, and cax3-2") seedlings show less sensitive to ethylene. "CAX1" and "CAX3" mutants have about 40-50% longer hypocotyls and primary roots in the presence of 0.5 mM ACC although their germination rates are the same. In contrast, "cax1" and "cax3" mutant seeds are similarly hypersensitive to calcium and ABA during germination, whereas those mutants show less sensitive to ABA inhibition of root elongation in seedling development. Microarray analysis indicates that deletion of "CAX1" and "CAX3" cause down- or up-regulation of similar groups of genes encoding several ethylene-response element binding proteins (EREBP), suggesting both "CAX1" and "CAX3" regulate similar components in ethylene- and ABA-mediated signaling pathway. Interestingly, our data also show that "cax1-1, cax3-1," and "cax3-2" seed germination rates decreased about 50% compared with wild type in response to 4-6% sucrose. Since sucrose stress, ABA, and ethylene signals generally can evoke a cytosolic Ca(2+) spiking, and sucrose stress involves ABA and ethylene pathways, we propose that CAX1 and CAX3 are involved in ABA and ethylene signaling by regulating cytosolic Ca(2+) homeostasis.