EDITORIAL published: 24 March 2020 doi: 10.3389/fpls.2020.00301 Editorial: Illuminating Carotenoid Synthesis and Plastid Transition in Plants Claudia Renate Stange 1*, Manuel Rodriguez-Concepcion 2 and Li Li 3 1 Department of Biology, University of Chile, Santiago, Chile, 2 Centre for Research in Agricultural Genomics, Barcelona, Spain, 3 Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, United States Keywords: plastid differentiation, carotenoid synthesis and degradation, metabolic flux, light, environmental cues Editorial on the Research Topic Illuminating Carotenoid Synthesis and Plastid Transition in Plants Because of the huge importance of carotenoids in plants and for human health, carotenoid metabolism and regulation have been studied extensively during the last 40 years. Carotenoids are produced and stored in plastids. Their contents are influenced not only by biosynthesis and degradation rates but also by the storage capacity of the plastid (which depends on the plastid type) and external cues such as light (which regulates the expression of biosynthetic genes and modulates plastid differentiation). Carotenoid accumulation also impacts plastid identity, and some of their degradation products are biologically active molecules that modulate many plant developmental processes. This Research Topic focuses on recent research done in these areas. A review article summarizes current knowledge on transcriptional regulation of carotenoid biosynthesis including nearly all regulators identified to date in photosynthetic tissues, fruits, seeds, flowers, and storage roots. Future research perspectives emphasize on broadening the diversity of “model” systems for carotenoid research and integrating multi-omics data to identify additional Edited and reviewed by: Kazuki Saito, carotenogenic transcriptional regulators and to map regulatory networks (Stanley and Yuan). RIKEN Center for Sustainable These strategies, together with testing the function of known carotenogenic regulators discovered Resource Science (CSRS), Japan from one species in other distantly related species, will provide insights to fill the gaps on the *Correspondence: understanding of transcriptional regulation of carotenoid biosynthesis in plants. Claudia Renate Stange Contributors of this Research Topic also show that light deprivation in Citrus species accelerates cstange@uchile.cl peel degreening, chlorophyll degradation while reducing carotenoid contents (Lado et al.). Fruit shading downregulates the expression of key carotenogenic genes, but levels of transcripts for Specialty section: enzymes responsible to cleave carotenoids for the formation of β-citraurin or to supply carotenoid This article was submitted to precursors via the methylerythritol 4-phosphate (MEP) pathway were not substantially affected by Plant Metabolism and Chemodiversity, light deprivation. Their findings suggest that light stimulates carotenoid biosynthesis in the peel of a section of the journal citrus fruit, but that a light-independent regulation may also operate. Frontiers in Plant Science The Orange (OR) protein as a DnaJE1 family chaperone protein exerts multiple functions in Received: 21 January 2020 governing carotenoid accumulation. OR regulates carotenoid biosynthesis by posttranslationally Accepted: 02 March 2020 regulating phytoene synthase (PSY, the first and main rate-determining enzyme of the pathway). Published: 24 March 2020 Moreover, OR promotes stable storage by inducing the formation of chromoplasts and Citation: preventing carotenoid degradation. In this Research Topic, a review article describes our current Stange CR, Rodriguez-Concepcion M and Li L (2020) Editorial: Illuminating understanding of the molecular and biochemical bases underlying OR-induced carotenoid Carotenoid Synthesis and Plastid accumulation and the potential of modifying the gene and chromoplast sink toward the Transition in Plants. development of healthy food for a growing population (Osorio). Additionally, a mini-review Front. Plant Sci. 11:301. emphasizes the role of the carotenogenic metabolic flux, its association with the “golden SNP” of doi: 10.3389/fpls.2020.00301 melon CmOR, and its arrest during the process of melon fruit ripening to illuminate chromoplast Frontiers in Plant Science | www.frontiersin.org 1 March 2020 | Volume 11 | Article 301 Stange et al. Plant Carotenoid Synthesis and Plastid Transition differentiation and carotenoid accumulation (Feder et al.). on their role in plant growth, development, and stress Investigation of three differently spliced transcripts of cauliflower responses (Felemban et al.). BoOR suggests the requirement of OR dimerization for OR Future novel research focused on plastid differentiation and protein stability in planta, the need of simultaneous presence light-regulated processes will help further deciphering carotenoid of PSY interaction-domains for the holdase function of OR, biosynthesis and carotenogenic metabolic flux during plant and the possible formation of various BoOR heterodimers for growth and development. an enhanced activity on carotenoid accumulation (Welsch In summary, this Research Topic provides valuable clues to et al.). Besides OR, other chaperones and the Clp protease advance in our understanding of the multi-level regulation of complex are known to influence PSY proteostasis and carotenoid carotenoid biosynthesis, storage, and degradation by endogenous accumulation. In particular, both OR and Hsp70 chaperones and environmental cues. impact the accumulation of carotenoids in transgenic tomato ripe fruit. However, the resulting carotenoid profile and AUTHOR CONTRIBUTIONS chromoplast ultrastructure are different, suggesting that different chaperone families target different processes related to CS, LL, and MR-C wrote the manuscript. carotenoid metabolism and accumulation during tomato fruit ripening (D’Andrea and Rodriguez-Concepcion). FUNDING Carotenoids are required for chloroplast biogenesis. A study proposes that the MEP-independent mevalonate (MVA) This study was supported by Fondecyt 1180747 (CS). pathway, which is not localized in plastids but in the cytosol, Conflict of Interest: The authors declare that the research was conducted in the might provide GGPP isoprenoid intermediate which is then absence of any commercial or financial relationships that could be construed as a transported into plastids for carotenoids and chloroplast potential conflict of interest. biogenesis in Arabidopsis embryos (Vranová et al.). Besides the well-known carotenoid-derived phytohormones (i.e., Copyright © 2020 Stange, Rodriguez-Concepcion and Li. This is an open-access ABA and strigolactones) and signaling molecules (e.g., beta- article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided cyclocitral), novel apocarotenoids are being identified to the original author(s) and the copyright owner(s) are credited and that the original function as biologically-active regulators. A review paper publication in this journal is cited, in accordance with accepted academic practice. describes the biosynthesis and biological functions of two No use, distribution or reproduction is permitted which does not comply with these of these regulatory apocarotenoids, and provides insights terms. Frontiers in Plant Science | www.frontiersin.org 2 March 2020 | Volume 11 | Article 301