A cis-carotene derived apocarotenoid regulates etioplast and chloroplast development

Carotenoids are a core plastid component and yet their 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 and their derivatives under varied dark-light regimes. A forward genetics approach revealed how an epistatic interaction between a z-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 retrograde signal, as chemical inhibition of carotenoid cleavage dioxygenase activity restored PLB formation in ccr2 etioplasts during skotomorphogenesis. The apocarotenoid acted in parallel to the repressor of photomorphogenesis, DEETIOLATED1 (DET1), to transcriptionally regulate PROTOCHLOROPHYLLIDE OXIDOREDUCTASE (POR), PHYTOCHROME INTERACTING FACTOR3 (PIF3) and ELONGATED HYPOCOTYL5 (HY5). The unknown apocarotenoid signal restored POR protein levels and PLB formation in det1, thereby controlling plastid development

Light-limited photosynthesis under energy-saving film decreases eggplant yield

Glasshouse films with adjustable light transmittance and energy-efficient designs have the potential to reduce (up to 80%) the high energy cost for greenhouse horticulture operations. Whether these films compromise the quantity and quality of light transmission for photosynthesis and crop yield remains unclear. A “Smart Glass” film ULR-80 (SG) was applied to a high-tech greenhouse horticulture facility, and two experimental trials were conducted by growing eggplant (Solanum melongena) using commercial vertical cultivation and management practices. SG blocked 85% of ultraviolet (UV), 58% of far-red, and 26% of red light, leading to an overall reduction of 19% in photosynthetically active radiation (PAR, 380–699 nm) and a 25% reduction in total season fruit yield. There was a 53% (season mean) reduction in net short-wave radiation (radiometer range, 385–2,105 nm upward; 295–2,685 nm downward) that generated a net reduction of 8% in heat load and reduced water and nutrient consumption by 18%, leading to improved energy and resource use efficiency. Eggplant adjusted to the altered SG light environment via decreased maximum light-saturated photosynthetic rates (Amax) and lower xanthophyll de-epoxidation state. The shift in light characteristics under SG led to reduced photosynthesis, which may have reduced source (leaf) to sink (fruit) carbon distribution, increased fruit abortion and decreased fruit yield, but did not affect nutritional quality. We conclude that SG increases energy and resource use efficiency, without affecting fruit quality, but the reduction in photosynthesis and eggplant yield is high. The solution is to re-engineer the SG to increase penetration of UV and PAR, while maintaining blockage of glasshouse heat gain

Plant apocarotenoids : from retrograde signaling to interspecific communication

Carotenoids are isoprenoid compounds synthesized by all photosynthetic and some nonphotosynthetic organisms. They are essential for photosynthesis and contribute to many other aspects of a plant's life. The oxidative breakdown of carotenoids gives rise to the formation of a diverse family of essential metabolites called apocarotenoids. This metabolic process either takes place spontaneously through reactive oxygen species (ROS) or is catalyzed by enzymes generally belonging to the carotenoid cleavage dioxygenase (CCD) family. Apocarotenoids include the phytohormones abscisic acid (ABA) and strigolactones (SLs), signaling molecules, and growth regulators. ABA and SLs are vital in regulating plant growth, development, and stress response. SLs are also an essential component in plants’rhizospheric communication with symbionts and parasites. Other apocarotenoid small molecules, such as blumenols, mycorradicins, zaxinone, anchorene, β-cyclocitral, βcyclogeranic acid, β-ionone, and loliolide, are involved in plant growth and development, and/or contribute to different processes, including arbuscular mycorrhiza (AM) symbiosis, abiotic stress response, plant-plant and plant-herbivore interactions, and plastid retrograde signaling. There are also indications for the presence of structurally unidentifiedlinearcis-carotene-derived apocarotenoids (LCDAs), which are presumed to modulateplastid biogenesis and leaf morphology, among other developmental processes. Here, we provide an overview on the biology of old, recently discovered, and supposed plant apocarotenoid signaling molecules, describing their biosynthesis, developmental and physiological functions, and role as a messenger in plants’ communication

Epigenetic control of carotenogenesis during plant development

Carotenoids are secondary metabolites synthesized in plastids that function in photosynthesis, photoprotection, growth and development of plants. Carotenoids contribute to the yellowish, orange and pinkish-red hues of leaves, flowers and fruits, as well as various aromas. They provide substrates for the biosynthesis of phytohormones and are cleavable into smaller apocarotenoids that function as retrograde signals and/or mediate intracellular communication as well as regulate gene transcription and/or protein translation. Carotenoid biosynthesis and gene regulation are tightly coordinated with tissue-specific plastid differentiation, seedling morphogenesis, fruit development, and prevailing environmental growth conditions such as light, temperature and mycorrhizal interactions. In the last decade, epigenetic processes have been linked to the regulation of carotenoid biosynthesis, accumulation and degradation during plant development. Next-generation sequencing approaches have shed new light on key rate-limiting steps in carotenoid pathways targeted by epigenetic modifications that synchronize carotenoid accumulation with plastid development and morphogenesis. We discuss how histone modifications (methylation and acetylation), DNA methylation and demethylation, as well as small RNA gene silencing processes can modulate carotenoid biosynthesis, accumulation and apocarotenoid generation throughout the plants’ life cycle: from seed germination to fruit morphogenesis. This review highlights how apocarotenoid signals regulate plastid biogenesis and gene expression in sync with chromatin alterations during skotomorphogenesis and photo-morphogenesis. We provide a new perspective based upon emerging evidence that supports a likely role for carotenoids in contributing to the programming and/or maintenance of the plants' epigenetic landscape

cis/trans carotenoid extraction, purification, detection, quantification and profiling in plant tissues

Reverse phase high-performance liquid chromatography (HPLC) is the method of choice used in biological, health, and food research to identify, quantify, and profile carotenoid species. The identification and quantification of cis- and/or trans-carotene and xanthophyll isomers in plant tissues can be affected by the method of sample preparation and extraction, as well as the HPLC column chemistry and the solvent gradient. There is a high degree of heterogeneity in existing methods in terms of their ease, efficiency, and accuracy. We describe a simple carotenoid extraction method and two different optimised HPLC methods utilizing C18 or C30 reverse-phase columns. We outline applications, advantages, and disadvantages for using these reverse phase columns to detect xanthophylls and cis-carotenes in wild-type photosynthetic leaves and mutant dark-grown etiolated seedlings, respectively. Resources are provided to profile individual species based upon their spectral properties and retention time, as well as quantify carotenoids by their composition and absolute levels in different plant tissues

Light-altering cover materials and sustainable greenhouse production of vegetables : a review

Greenhouse horticulture (protected cropping) is essential in meeting increasing global food demand under climate change scenarios by ensuring sustainability, efficiency, and productivity. Recent advances in cover materials and photovoltaic technologies have been widely examined in greenhouses to improve light transmission and solar energy capture with promoting energy-saving. We review the studies on advanced greenhouse cover materials with variable light transmittance, the effects of which on leaf photosynthesis, physiology, and yield. We provide insights into the potential key biological processes of crops responding to these light changes, specifically light receptors, signal transduction, nutrient biosynthesis pathways (e.g., carotenoids, antioxidant compounds) during fruit development and ripening. A better understanding of greenhouse cover materials with a focus towards energy-efficient cover materials equipped in greenhouse is an opportunity for better yield and higher nutrient products production in vegetables in response to global climate challenges. Interdisciplinary research on the application of novel cover materials in greenhouses and biological investigation of light-induced physiology and nutrient formation in vegetables may promote yield and health attributes for protected cultivation of vegetables with energy use efficiency