AUTHOR=Ibata Harue , Nagatani Akira , Mochizuki Nobuyoshi 

TITLE=CHLH/GUN5 Function in Tetrapyrrole Metabolism Is Correlated with Plastid Signaling but not ABA Responses in Guard Cells

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.01650

DOI=10.3389/fpls.2016.01650

ISSN=1664-462X

ABSTRACT=<p>Expression of <italic>Photosynthesis-Associated Nuclear Genes</italic> (<italic>PhANGs</italic>) is controlled by environmental stimuli and plastid-derived signals (“plastid signals”) transmitting the developmental and functional status of plastids to the nucleus. <italic>Arabidopsis genomes uncoupled</italic> (<italic>gun</italic>) mutants exhibit defects in plastid signaling, leading to ectopic expression of <italic>PhANGs</italic> in the absence of chloroplast development. <italic>GUN5</italic> encodes the plastid-localized Mg-chelatase enzyme subunit (CHLH), and recent studies suggest that CHLH is a multifunctional protein involved in tetrapyrrole biosynthesis, plastid signaling and ABA responses in guard cells. To understand the basis of CHLH multifunctionality, we investigated 15 <italic>gun5</italic> missense mutant alleles and transgenic lines expressing a series of truncated CHLH proteins in a severe <italic>gun5</italic> allele (<italic>cch</italic>) background (tCHLHs, 10 different versions). Here, we show that Mg-chelatase function and plastid signaling are generally correlated; in contrast, based on the analysis of the <italic>gun5</italic> missense mutant alleles, ABA-regulated stomatal control is distinct from these two other functions. We found that none of the tCHLHs could restore plastid-signaling or Mg-chelatase functions. Additionally, we found that both the C-terminal half and N-terminal half of CHLH function in ABA-induced stomatal movement.</p>