AtMHX is an auxin and ABA-regulated transporter whose expression pattern suggests a role in metal homeostasis in tissues with photosynthetic potential
Ora David-Assael A , Irina Berezin A , Noa Shoshani-Knaani A , Helen Saul A , Talya Mizrachy-Dagri A , Jianxin Chen A , Emil Brook A and Orit Shaul A BA The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel.
B Corresponding author. Email: orsha@mail.biu.ac.il
Functional Plant Biology 33(7) 661-672 https://doi.org/10.1071/FP05295
Submitted: 5 December 2005 Accepted: 19 April 2006 Published: 3 July 2006
Abstract
AtMHX is a vacuolar transporter encoded by a single gene in Arabidopsis thaliana (L.) Heynh. It exchanges protons with Mg2+, Zn2+, and Fe2+ ions. Proper homeostasis of these metals is essential for photosynthesis and numerous enzymatic reactions. In particular, very little is known about mechanisms involved in Mg2+ homeostasis in plants. Expression analysis using reporter-gene constructs suggested that AtMHX functions in metal homeostasis mainly in tissues with photosynthetic potential. This balancing is conducted by expression in the vascular region, the cortex of stems, trichomes, and hydathodes. Expression in stems is developmentally regulated, suggesting that minerals are accumulated in the upper regions of young stems, and are released during silique development. Mineral content in different stem parts was consistent with this possibility. Expression was induced by auxin and ABA, but not by the metal content of the growth medium, suggesting that expression is mainly regulated by endogenous developmental programs. AtMHX exhibits two distinguished regulatory properties. Its leader intron is absolutely essential for expression, and mediates an 86-fold enhancement of expression. This enhancement is the highest reported thus far for any dicot intron. Another remarkable feature is that a repetitive genomic element of 530 bp (or part of it) functions as an enhancer.
Keywords: Arabidopsis, iron, leader intron, magnesium, repetitive element, vacuolar transporter, zinc.
Acknowledgments
The authors thank Daniel R Gallie for the pJD330 plasmid, and Roni Aloni and Simcha Lev-Yadun for helpful discussions. This research was supported by the Israel Science Foundation (grants no. 437 / 99–1 and 682 / 03).
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