AUTHOR=Park Joon-Heum , Tran Lien H. , Jung Sunyo 

TITLE=Perturbations in the Photosynthetic Pigment Status Result in Photooxidation-Induced Crosstalk between Carotenoid and Porphyrin Biosynthetic Pathways

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.01992

DOI=10.3389/fpls.2017.01992

ISSN=1664-462X

ABSTRACT=<p>Possible crosstalk between the carotenoid and porphyrin biosynthetic pathways under photooxidative conditions was investigated by using their biosynthetic inhibitors, norflurazon (NF) and oxyfluorfen (OF). High levels of protoporphyrin IX (Proto IX) accumulated in rice plants treated with OF, whereas Proto IX decreased in plants treated with NF. Both NF and OF treatments resulted in greater decreases in MgProto IX, MgProto IX methyl ester, and protochlorophyllide. Activities and transcript levels of most porphyrin biosynthetic enzymes, particularly in the Mg-porphyrin branch, were greatly down-regulated in NF and OF plants. In contrast, the transcript levels of <italic>GSA, PPO1</italic>, and <italic>CHLD</italic> as well as <italic>FC2</italic> and <italic>HO2</italic> were up-regulated in NF-treated plants, while only moderate increases in <italic>FC2</italic> and <italic>HO2</italic> were observed in the early stage of OF treatment. Phytoene, antheraxanthin, and zeaxanthin showed high accumulation in NF-treated plants, whereas other carotenoid intermediates greatly decreased. Transcript levels of carotenoid biosynthetic genes, <italic>PSY1</italic> and <italic>PDS</italic>, decreased in response to NF and OF, whereas plants in the later stage of NF treatment exhibited up-regulation of <italic>BCH</italic> and <italic>VDE</italic> as well as recovery of <italic>PDS</italic>. However, perturbed porphyrin biosynthesis by OF did not noticeably influence levels of carotenoid metabolites, regardless of the strong down-regulation of carotenoid biosynthetic genes. Both NF and OF plants appeared to provide enhanced protection against photooxidative damage, not only by scavenging of Mg<italic>-</italic>porphyrins, but also by up-regulating <italic>FC2, HO2</italic>, and Fe-chelatase, particularly with increased levels of zeaxanthin via up-regulation of <italic>BCH</italic> and <italic>VDE</italic> in NF plants. On the other hand, the up-regulation of <italic>GSA, PPO1</italic>, and <italic>CHLD</italic> under inhibition of carotenogenic flux may be derived from the necessity to recover impaired chloroplast biogenesis during photooxidative stress. Our study demonstrates that perturbations in carotenoid and porphyrin biosynthesis coordinate the expression of their biosynthetic genes to sustain plastid function at optimal levels by regulating their metabolic flux in plants under adverse stress conditions.</p>