1. China State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, 100094 Beijing, China
2. These authors contributed equally to this work.

Correspondence to: Da-Peng Zhang¹ The sequence of the cDNA encoding part of CHLH is deposited in GenBank under accession number DQ376081. Correspondence and requests for materials should be addressed to D.P.Z. (Email: zhangdp@sohu.net).

Abstract

Abscisic acid (ABA) is a vital phytohormone that regulates mainly stomatal aperture and seed development, but ABA receptors involved in these processes have yet to be determined. We previously identified from broad bean an ABA-binding protein (ABAR) potentially involved in stomatal signalling, the gene for which encodes the H subunit of Mg-chelatase (CHLH), which is a key component in both chlorophyll biosynthesis and plastid-to-nucleus signalling. Here we show that Arabidopsis ABAR/CHLH specifically binds ABA, and mediates ABA signalling as a positive regulator in seed germination, post-germination growth and stomatal movement, showing that ABAR/CHLH is an ABA receptor. We show also that ABAR/CHLH is a ubiquitous protein expressed in both green and non-green tissues, indicating that it might be able to perceive the ABA signal at the whole-plant level.

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