ARS | Publication request: REGULATION OF CAX1, AN ARABIDOPSIS CA2+/H+ ANTIPORTER: IDENTIFICATION OF ANN-TERMINAL AUTOINHIBITORY DOMAIN

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 2001
Publication Date: November 4, 2001

Interpretive Summary: We wanted to understand more about how nutrients move through plants, which would enable us to figure out how to move additional amounts of nutrients into plant-based foods. For example, if researchers can find a way to pump up the amount of calcium in vegetables, that would enhance their nutritional quality and benefit human health, especially children's growing gbones. Many children these days drink a lot of soda, but not enough calcium-rich milk. For our purposes here, we understand that we need to go to the level of the plant gene that relates to the transport of nutrients. We selected a strain of yeast and studied the CAX gene, which is directly involved in the movement of nutrients through plants to storage closets in their cells. Our goal was to understand how the CAX gene is controlled. Our findings suggest that this important plant transporter, which moves nutrients into storage sites in plant cells, is controlled by a unique mechanism. Once we understand the mechanism of the control, we can figure out how to expand the amount of space in plants' nutrient cupboards, in order to produce more nutrient-rich plant-based foods. The information gained from this study has great value in terms of pursuing genetic ways to maximize the nutritional benefit children reap from the foods they eat for optimal growth and health.

Technical Abstract: Regulation of Ca2+ transport determines the duration of a Ca2+ signal and hence the nature of the biological response. Ca2+/H+ antiporters such as CAX1 (cation exchanger 1), play a key role in determining cytosolic Ca2+ levels. Analysis of a full-length CAX1 clone suggested that the CAX1 open reading frame contains an additional 36 amino acids at the N-terminus not found in the original clone identified by suppression of yeast vacuolar Ca2+ transport mutants. The long CAX1 (lCAX1) could not suppress the yeast Ca2+ transport defects despite localization to the yeast vacuole. Calmodulin could not stimulate lCAX1 Ca2+/H+ transport in yeast; however, minor alterations in the 36 amino acid region restored Ca2+/H+ transport. Sequence analysis suggests that a 36 amino acid N-terminal regulatory domain may be present in all Arabidopsis CAX-like genes. Together, these results suggest a structural feature involved in regulation of Ca2+/H+ antiport.