Abstract
Expression of nuclear-encoded photosynthesis-related genes is greatly affected by the developmental and functional status of plastids. Retrograde signals (plastid signals) derived from plastids are hypothesized for this regulation. Although the involvement of tetrapyrrole biosynthesis has been strongly suggested, the entity of the signal is still obscure. Mg-chelatase H subunit (CHLH), that is also designated GUN5/ABAR, is a multifunctional protein involved in tetrapyrrole biosynthesis, plastid signaling and ABA signaling as a receptor. We therefore tested possible interaction between plastid signal and ABA. As previously reported (C. Voigt et al. Physiol. Plant, 2009), low dosage of ABA partially restores plastid signal. We are currently testing the effect of ABA in gun mutants including gun5 mutant alleles. To understand the domain structure of CHLH/GUN5/ABAR protein, we expressed modified CHLH protein in Arabidopsis wild type and gun5 mutants, and examined these transgenic plants for tetrapyrrole biosynthesis, plastid signaling and ABA responses. We would also like to present our recent progress on the mutant screening in plastid signaling using FOX-hunting system.
