Biology subjects

Ezquerro, M.

Publications and source records attributed to Ezquerro, M..

4 recordsLinked to original sources

bioRxiv2025

Loss of tomato geranylgeranyl diphosphate synthase 2 increases monoterpenoid levels and enhances immune responses to bacterial infection

Many plastidial isoprenoids, including diterpenes and photosynthesis-related isoprenoids such as carotenoids and chlorophylls, derive from C20 geranylgeranyl diphosphate (GGPP), produced by GGPP synthase (GGPPS) enzymes. Heterodimers of GGPPS and non-catalytic type I small subunit (SSU-I) proteins produce C10 geranyl diphosphate (GPP), the precursor of monoterpenes. Three plastidial GGPPS isoforms, referred to as SlG1-3, are present in tomato (Solanum lycopersicum). Here we explored their contribution to the production of volatile organic compounds (VOCs) of isoprenoid origin under normal conditions and in response to infection with Pseudomonas syringae pathovar tomato (Pst). Edited lines lacking SlG2 showed a distinctive VOC profile compared to unedited (WT) plants and mutants impaired in SlG1 or SlG3. In particular, only slg2 mutants showed constitutively increased levels of GPP-derived hydroxylated monoterpenes (HMTPs). Upon Pst infection, slg2 plants accumulated higher levels of salicylic acid (SA) and exhibited increase resistance compared to WT controls, resulting in reduced levels of VOCs associated to cell death. Our findings suggest that SlG2 regulates GPP synthesis, potentially by specifically competing with other GGPPS isoforms for heterodimerization with SSU-I. Increased GPP production in slg2 plants could lead to higher HMTPs levels, which may result in elevated SA content, and subsequently enhanced protection against bacterial infection.

plant biology↗

bioRxiv2025

Activation of alternative oxidase ensures carbon supply for ethylene and carotenoid biosynthesis during tomato fruit ripening

Tomato (Solanum lycopersicum) is a climacteric fruit displaying a peak of respiration at the onset of ripening accompanied by increased synthesis of ethylene and carotenoid pigments. Chromoplast and mitochondrial respiration participate at different stages of fruit ripening, but their in vivo regulation and function remains unclear. We determined the in vivo activities of the mitochondrial alternative oxidase (AOX) and cytochrome oxidase pathways and quantified the levels of respiratory- and ripening-related gene transcripts, primary metabolites and carotenoids in ripening tomato fruits with or without a functional chromorespiration. Furthermore, we carried out physiological, molecular and metabolic analyses of CRISPR-Cas9 mutants defective in AOX1a, the main AOX isoform up-regulated during tomato fruit ripening. We confirmed that PTOX-dependent chromorespiration is only relevant at late stages of ripening and found that in vivo AOX activity significantly increased at the breaker stage, becoming the main contributor to climacteric respiration when ripening is unleashed. This activation did not correlate with gene expression but was likely due to increased levels of AOX activators such as pyruvate (a metabolic precursor of carotenoids), 2-oxoglutarate and succinate. A strong alteration of ripening-related metabolites was observed in aox1a mutant fruits, highlighting a key role of the AOX pathway at the onset of ripening. Our data suggest that increased supply of TCA cycle intermediates at climacteric stage allosterically enhance AOX activity, thus allowing the reoxidation of NAD(P)H to ensure carbon supply for triggering ethylene and carotenoid biosynthesis.

plant biology↗

bioRxiv2022

Tomato geranylgeranyl diphosphate synthase isoform 1 specifically interacts with phytoene synthase isoform 3 to produce strigolactones in tomato roots.

O_LICarotenoids are photoprotectant pigments and precursors of the hormones abscisic acid (ABA) and strigolactones (SL). Carotenoids are produced in plastids from geranylgeranyl diphosphate (GGPP), which is diverted to the carotenoid pathway by phytoene synthase (PSY). In tomato (Solanum lycopersicum), 3 genes encode plastid-targeted GGPP synthases (SlG1 to 3) and 3 genes encode PSY isoforms (PSY1 to 3). C_LIO_LIHere we investigated the function of SlG1 by generating loss-of-function lines and combining their metabolic and physiological phenotypes with gene co-expression and co-immunoprecipitation analyses. C_LIO_LILeaves and fruits of slg1 lines showed a wild-type phenotype in terms of isoprenoid accumulation, photosynthesis and development. Consistently, SlG1 is co-expressed with PSY3 and other genes involved in the production of carotenoids and SL (but not ABA) only in roots. SlG1 was also found to physically interact with the root-specific PSY3 isoform (and not with PSY1 and PSY2). Root SL (but not ABA) levels were reduced in slg1 lines. C_LIO_LIOur results confirm a specific role of SlG1 in SL production in combination with PSY3. This role appears to be restricted to roots as slg1 plants do not exhibit the shoot phenotype displayed by other SL-deficient mutants. C_LI

plant biology↗

bioRxiv2022

Overlapping and specialized roles of tomato phytoene synthase isoforms PSY1 and PSY2 in carotenoid and ABA production

Carotenoids are plastidial isoprenoids required for photosynthesis and production of hormones such as abscisic acid (ABA) in all plants. In tomato (Solanum lycopersicum), carotenoids also provide color to flowers and ripe fruit. Phytoene synthase (PSY) catalyzes the first and main flux-controlling step of the carotenoid pathway. Three PSY isoforms are present in tomato, PSY1 to 3. Mutants have shown that PSY1 is the isoform providing carotenoids for fruit pigmentation but it is dispensable in photosynthetic tissues. No mutants are available for PSY2 or PSY3, but their expression profiles suggest a main role for PSY2 in leaves and PSY3 in roots. To further investigate isoform specialization with genetic tools, we created tomato edited lines defective in PSY1 and PSY2 in the MicroTom background. The albino phenotype of lines lacking both PSY1 and PSY2 confirmed that PSY3 does not contribute to carotenoid biosynthesis in shoot tissues. Our work further shows that carotenoid production in tomato shoots relies on both PSY1 and PSY2 but with different contributions in different tissues. PSY2 is the main isoform for carotenoid biosynthesis in leaf chloroplasts, but the supporting role of PSY1 is particularly important under high light. PSY2 also contributes to the production of carotenoids in flower petals and, to a lower extent, fruit chromoplasts. Most interestingly, our results demonstrate that fruit growth and ripening is controlled by ABA produced in the pericarp from PSY1-derived precursors whereas PSY2 provides precursors for ABA synthesis in seeds to control germination.

plant biology↗