Pathway discovery in apocarotenoid metabolism: focus on putative zaxinone synthase enzymes in tomato
Author(s)
Date Issued
2025
Type
conferenceObject
Abstract
In recent years, the identification of genes involved in the production and regulati
specialized metabolites has led to the discovery of key molecules and new metabolic pathways
that shape plant fitness, stress tolerance, and interactions with the environment. Among these,
carotenoid-derived metabolic pathways mediated by Carotenoid Cleavage Dioxyge
enzymes (CCDs) contribute to the biosynthesis of several apocarotenoids, a diverse class
metabolites that includes phytohormones, signal molecules, chromophores and
constituents; thus, enabling the characterization of novel agronomic traits in industrial crops
such as Solanum lycopersicum L.
In addition to the six well-characterized CCD subfamilies (NCED, CCD1, CCD2, CCD4, CCD7, CCD8),
a seventh subfamily, named ZAS (zaxinone synthase), has recently been identified inOryza sativa.
Functional studies showed that two rice ZAS, OsZAS and OsZAS2, cleave the apocarotenoid β-apo-
10'-zeaxanthinal (C27) yielding zaxinone (C18). Zaxinone is an important growth regulat
apocarotenoid involving in plant development, arbuscular mycorrhizal (AM) symbiosis
modulation of strigolactone levels in rice. Metabolic findings revealed that zaxinone is a
present in tomato, prompting our interest in exploring its function and biosynthetic pathway in
this species too. Through BLASTp researches againstS. lycopersicum reference proteome, we
identified three putative orthologues of OsZAS in tomato genome: SlZAS, SlZAS-like 1 and SlZAS-
like 2. To evaluate their functions, full-length cDNAs were expressed as thioredoxin fusion inE.
coli cells and in vitro bacterial assays were performed. Among these, SlZAS displayed a cle
activity in converting β-apo-10'-zeaxanthinal to zaxinone in our experimental conditions. Thi
activity, together with the chloroplasts-associated localization, support its expected role
carotenoid-derived metabolic pathways. To further investigate theirin vivo functions, different
CRISPR/Cas9 knock-out tomato lines were generated.
Specifically, phenotypic characterization of zasloss-of-function mutants (T2 generation) revealed
reduced shoot growth and a less developed root system compared towild-type plants. Moreover,
a strong reduction of zaxinone level was detected in mutant root system compared towild-type,
highlighting its role in zaxinone biosynthesis. Furthermore, the analysis of polar and non-polar
metabolic profiles in tomato zas mutants has been conducted, revealing indications of possible
changes in key metabolites associated with physiological and ecological functions.
Further investigations and analyses will completely elucidate the enzymatic functions of these
genes and clarify the zaxinone biosynthetic pathway in tomato as well, providing new insight into
apocarotenoid metabolism in solanaceous crops and new prospects for advanced breeding and
the development of novel and more resilient varieties.
Conference(s)
Italian Society of Agricultural Genetics holds its LXVIII Annual Congress