Biology subjects

Alagoz, Y.

Publications and source records attributed to Alagoz, Y..

5 recordsLinked to original sources

bioRxiv2024

The LYCOPENE EPSILON CYCLASE untranslated mRNA leader modulates carotenoid feedback and post-transcriptional regulation

Metabolic feedback is proposed to modulate nuclear gene expression and carotenoid biosynthesis in plastids, however few mechanisms have been identified so far in plants. Utilising mutants, overexpression lines, and chemical inhibitors, we demonstrate that Arabidopsis LYCOPENE EPSILON CYCLASE ({varepsilon}LCY) mRNA levels correlate with changes in {beta}-carotenoid accumulation. Transgenic seedlings harbouring the{varepsilon} LCY 5 leader sequence fused to FIREFLY LUCIFERASE (FiLUC) showed reporter responsiveness to metabolic feedback triggered by norflurazon or loss-of-function in the CAROTENOID ISOMERASE (CRTISO). The{varepsilon} LCY 5UTR harboured three alternative transcription start sites (TSS). The most abundant -133bp sequence generated in dark and light grown seedlings harboured a 5 conserved domain (CD) with other Brassicaceae species and a viral internal ribosome entry site (IRES) proximal to the start codon. In silico modelling predicted the 5UTR formed two energetically separated RNA structural probabilities having a minimal free energy consistent with metabolite-binding RNA riboswitches that was distinguished by hairpin structures within the CD. Site-specific mutations were used to stabilize the 5UTR into a single RNA shape definition having negligible separation between the mountain plot structure prediction curves and a distal terminator-like hairpin structure. Stabilizing the 5UTR shape triggered the posttranscriptional repression of FiLUC activity enabled by the CaMV35S promoter in tobacco transient assays and stable transgenic Arabidopsis lines. The stabilised shape fragment became responsive to metabolic feedback induced by norflurazon and in crtiso mutant etiolated and de-etiolated seedlings. The{varepsilon} LCY 5UTR resembles a conformational RNA regulatory switch harbouring a posttranscriptional expression platform and aptamer domain responsive to carotenoid-mediated feedback signalling.

plant biology↗

bioRxiv2023

Abscisic acid inhibits germination of Striga seeds and is released by them as a rhizospheric signal providing competitive advantage and supporting host infestation

O_LISeeds of the root parasitic plant Striga hermonthica undergo a conditioning process under humid and warm environments before germinating in response to host-released stimulants, particularly strigolactones (SLs). The plant hormone abscisic acid (ABA) regulates different growth and developmental processes, and stress response; however, its role during Striga seed germination and early interactions with host plants is under-investigated. C_LIO_LIHere, we show that ABA inhibited Striga seed germination and that hindering its biosynthesis induced conditioning and germination in unconditioned seeds, which was significantly enhanced by treatment with the SL analog rac-GR24. However, the inhibitory effect of ABA remarkably decreased during conditioning, confirming the loss of sensitivity towards ABA in later developmental stages. ABA measurement showed a significant reduction of its content during the early conditioning stage and a significant increase upon rac-GR24-triggered germination. We observed this increase also in released seed exudates, which was further confirmed by using the Arabidopsis ABA-reporter GUS marker line. C_LIO_LISeed exudates of germinated seeds, containing elevated levels of ABA, impaired the germination of surrounding Striga seeds in vitro and promoted root growth of a rice host towards germinated Striga seeds. Application of ABA as a positive control caused similar effects, indicating its function in Striga/Striga and Striga/host communications. C_LIO_LIIn summary, we show that ABA is an essential player during seed dormancy and germination processes in Striga and acts as a rhizospheric signal released by germinated parasitic seeds to provide a competitive advantage and support host infestation. C_LI Societal Impact StatementThe root parasitic plant Striga hermonthica is a severe threat to cereals yield, endangering global food security. Herein, we uncover a new role of the known plant hormone abscisic acid (ABA) as a rhizospheric signal released by germinated Striga seeds, allowing them to better compete with surrounding un-conditioned seeds and facilitating host infestation. Our findings can help in developing strategies to control this parasite and mitigate its negative impact on the food supply and income of smallholder farmers.

plant biology↗

bioRxiv2023

Reducing PSY activity fine tunes threshold levels of a cis-carotene-derived signal that regulates the PIF3/HY5 module and plastid biogenesis

PHYTOENE SYNTHASE (PSY) is a rate-limiting enzyme catalysing the first committed step of carotenoid biosynthesis, and changes in PSY gene expression and/or protein activity alter carotenoid composition and plastid differentiation in plants. Here we identified four genetic variants of PSY (psy-4, psy-90, psy-130 and psy-145) using a forward genetics approach that rescued leaf virescence phenotypes displayed by the Arabidopsis CAROTENOID ISOMERASE (CRTISO) mutant ccr2 (carotenoid and chloroplast regulation 2) when grown under a shorter photoperiod. The four non-lethal mutations affected alternative splicing, enzyme-substrate interactions, and PSY:ORANGE multi-enzyme complex binding, constituting the dynamic posttranscriptional fine-tuning of PSY levels and activity without changing localization to the stroma and protothylakoid membranes. psy genetic variants did not alter overall total xanthophyll or cis-carotene accumulation in ccr2 yet reduced specific acyclic linear cis-carotenes linked to the biosynthesis of a yet-to-be-identified apocarotenoid signal. ccr2 psy variants modulated the ratio of PHYTOCHROME-INTERACTING FACTOR 3/ELONGATED HYPOCOTYL 5 (PIF3/HY5), displayed a normal PLB formation in etioplasts, and chlorophyll accumulation during seedling photomorphogenesis. Thus, suppressing PSY activity and impairing PSY:ORANGE protein interactions reveals how threshold specific cis-carotene levels can be fine-tuned through holoenzyme-metabolon interactions to control plastid development. HighlightsManipulation of the PHYTOENE SYNTHASE catalytic activity in concert with its regulatory protein, ORANGE, reduces threshold levels of acyclic linear cis-carotenes that signal control over plastid biogenesis in dark and light grown Arabidopsis seedlings

plant biology↗

bioRxiv2022

The Arabidopsis D27like1 is a novel Isomerase that Contributes to SL Biosynthesis and Negatively Impacts ABA Level

The enzyme DWARF27 (D27) catalyzes the reversible isomerization of all-trans- into 9-cis-{beta}-carotene, initiating strigolactone (SL) biosynthesis. Genomes of higher plants encode two D27-homologs, D27-like1 and -like2, with unknown functions. Here, we investigated the enzymatic activity and biological function of the Arabidopsis D27-like1. In vitro enzymatic assays and Expression in Synechocystis sp. PCC6803 revealed a yet not reported 13-cis/15-cis/9-cis- and a 9-cis/all-trans-{beta}-carotene isomerization. Although disruption of AtD27-like1 did not cause SL deficiency phenotypes, overexpression of AtD27-like1 in the Atd27 mutant restored the more-branching phenotype, indicating a contribution of AtD27-like1 to SL biosynthesis. Accordingly, generated Atd27 Atd27like1 double mutants showed more pronounced branching phenotype, compared to Atd27. The contribution of AtD27-like1 to SL biosynthesis is likely due to its formation of 9-cis-{beta}-carotene that was present at higher levels in AtD27-like1 overexpressing lines. In contrast, AtD27-like1 expression correlated negatively with the content of 9-cis-violaxanthin, a precursor of abscisic acid (ABA), in shoots. Consistently, ABA levels were higher in shoots and also in dry seeds of the Atd27like1 and Atd27 Atd27like1 mutants. Transgenic lines expressing {beta}-glucuronidase (GUS) driven by the AtD27LIKE1 promoter and transcript analysis performed with hormone-treated Arabidopsis seedlings unraveled that AtD27LIKE1 is expressed in different tissues and regulated ABA and auxin. Taken together, our work revealed a cis/cis-{beta}-carotene isomerase activity that affects the content of both cis-carotenoid derived plant hormones ABA and SLs.

plant biology↗

bioRxiv2019

A cis-carotene derived apocarotenoid regulates etioplast and chloroplast development

Carotenoids are core plastid components, yet a 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 under varied dark-light regimes. A forward genetics approach revealed how an epistatic interaction between a (-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 signal, as chemical inhibition of carotenoid cleavage dioxygenase activity restored PLB formation in ccr2 etioplasts during skotomorphogenesis. The apocarotenoid acted in parallel to the transcriptional repressor of photomorphogenesis, DEETIOLATED1 (DET1), to post-transcriptionally regulate PROTOCHLOROPHYLLIDE OXIDOREDUCTASE (POR), PHYTOCHROME INTERACTING FACTOR3 (PIF3) and ELONGATED HYPOCOTYL5 (HY5) protein levels. The apocarotenoid signal and det1 complemented each other to restore POR levels and PLB formation, thereby controlling plastid development. One-sentence summaryCarotenoids are not just required as core components for plastid biogenesis, they can be cleaved into an apocarotenoid signal that regulates etioplast and chloroplast development during extended periods of darkness.

plant biology↗