Plant apocarotenoids: from retrograde signaling to interspecific communication

Abstract

Summary Carotenoids are isoprenoid compounds synthesized by all photosynthetic and some non‐photosynthetic 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 or is catalyzed by enzymes generally belonging to the CAROTENOID CLEAVAGE DIOXYGENASE family. Apocarotenoids include the phytohormones abscisic acid and strigolactones (SLs), signaling molecules and growth regulators. Abscisic acid 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, β‐cyclogeranic acid, β‐ionone and loliolide, are involved in plant growth and development, and/or contribute to different processes, including arbuscular mycorrhiza symbiosis, abiotic stress response, plant–plant and plant–herbivore interactions and plastid retrograde signaling. There are also indications for the presence of structurally unidentified linear cis‐carotene‐derived apocarotenoids, which are presumed to modulate plastid 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 plant communication.

Plant cytochrome P450 plasticity and evolution

“…Strigolactones are involved in the symbiotic relation between land plants and soil arbuscular mycorrhiza and function as endogenous plant hormones (Moreno et al, 2021). In land plants, CYP711As (also known as MAX1) oxygenate the intermediate carlactone in strigolactone biosynthesis (Abe et al, 2014;Zhang et al, 2014Zhang et al, , 2018Yoneyama et al, 2018;Mori et al, 2020).…”

Iso‐anchorene is an endogenous metabolite that inhibits primary root growth in Arabidopsis

“…Alternatively, this metabolic process could take place spontaneously through ROS‐mediated carotenoid decay, as reported for β‐cyclocitral (Ramel et al , 2012). There are indications for the presence of numerous carotene‐derived metabolites, which are presumed to modulate lateral root formation, plastid biogenesis, leaf morphology, and other developmental processes (Moreno et al , 2020). Therefore, the present study revealed diapocarotenoids as candidates for carotene‐derived regulatory metabolites that modulate plant growth and development.…”

Assessing the Role of Carotenoid Cleavage Dioxygenase 4 Homoeologs in Carotenoid Accumulation and Plant Growth in Tetraploid Wheat

“…Among the growth and agronomic traits altered by ccd4 and/or pll mutations, mutations in the A or B subgenome homoeologs of CCD4 and PLL alone already had a significant impact on the convex hull area of seminal roots, the seminal root length (1)(2)(3)(4)(5), and the coleoptile length; these mutant phenotypes were exacerbated in ccd-A4 ccd-B4 pll-A pll-B where both A and B subgenome homoeologs were knocked out (Figures 5, 6). This suggests that the A and B subgenome homoeologs of CCD4 and/or PLL play distinct roles in controlling the above-mentioned traits.…”

“…In recent years, efforts have been directed toward enhancing the production of provitamin A carotenoids, particularly β-carotene, in wheat grains through breeding and biotechnology for improved vitamin A nutrition ( 2 ). However, provitamin A carotenoids produced in wheat grains may be subjected to degradation by carotenoid cleavage dioxygenases (CCDs) that cleave carotenoids (C 40 ) into smaller apocarotenoid molecules ( 3 ). Therefore, it is imperative to better understand the activity and function of CCDs in wheat grains for achieving a high level of provitamin A carotenoid accumulation.…”