PT  - JOURNAL ARTICLE
AU  - Christopher I Cazzonelli
AU  - Xin Hou
AU  - Yagiz Alagoz
AU  - John Rivers
AU  - Namraj Dhami
AU  - Jiwon Lee
AU  - Marri Shashikanth
AU  - Barry J Pogson
TI  - A <em>cis</em>-carotene derived apocarotenoid regulates etioplast and chloroplast development
AID  - 10.1101/528331
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 528331
4099  - http://biorxiv.org/content/early/2019/01/23/528331.short
4100  - http://biorxiv.org/content/early/2019/01/23/528331.full
AB  - Carotenoids are core plastid components, yet a regulatory function during plastid biogenesis remains enigmatic. A unique carotenoid biosynthesis mutant, carotenoid chloroplast regulation 2 (ccr2), that has no prolamellar body (PLB) and normal PROTOCHLOROPHYLLIDE OXIDOREDUCTASE (POR) levels, was used to demonstrate a regulatory function for carotenoids under varied dark-light regimes. A forward genetics approach revealed how an epistatic interaction between a (-carotene isomerase mutant (ziso-155) and ccr2 blocked the biosynthesis of specific cis-carotenes and restored PLB formation in etioplasts. We attributed this to a novel apocarotenoid signal, as chemical inhibition of carotenoid cleavage dioxygenase activity restored PLB formation in ccr2 etioplasts during skotomorphogenesis. The apocarotenoid acted in parallel to the transcriptional repressor of photomorphogenesis, DEETIOLATED1 (DET1), to post-transcriptionally regulate PROTOCHLOROPHYLLIDE OXIDOREDUCTASE (POR), PHYTOCHROME INTERACTING FACTOR3 (PIF3) and ELONGATED HYPOCOTYL5 (HY5) protein levels. The apocarotenoid signal and det1 complemented each other to restore POR levels and PLB formation, thereby controlling plastid development.One-sentence summary Carotenoids are not just required as core components for plastid biogenesis, they can be cleaved into an apocarotenoid signal that regulates etioplast and chloroplast development during extended periods of darkness.Abbreviationsccrcarotenoid and chloroplast regulationrccr2revertant of ccr2DAGdays after germinationYLyellow leafGLgreen leafNFnorflurazonACSapocarotenoid signal