Red and blue light differentially impact retrograde signalling and photoprotection in rice

Chloroplast-to-nucleus retrograde signalling (RS) is known to impact plant growth and development. In Arabidopsis, we and others have shown that RS affects seedling establishment by inhibiting deetiolation. In the presence of lincomycin, a chloroplast protein synthesis inhibitor that triggers RS, Arabidopsis light-grown seedlings display partial skotomorphogenesis with undeveloped plastids and closed cotyledons. By contrast, RS in monocotyledonous has been much less studied. Here, we show that emerging rice seedlings exposed to lincomycin do not accumulate chlorophyll but otherwise remain remarkably unaffected. However, by using high red (R) and blue (B) monochromatic lights in combination with lincomycin, we have uncovered a RS inhibition of length and a reduction in the B light-induced declination of the second leaf. Furthermore, we present data showing that seedlings grown in high B and R light display different non-photochemical quenching capacity. Our findings support the view that excess B and R light impact seedling photomorphogenesis differently to photoprotect and optimize the response to high-light stres

GENOMES UNCOUPLED1-independent retrograde signaling targets the ethylene pathway to repress photomorphogenesis

Altres ajuts: CERCA Programme/Generalitat de CatalunyaWhen germinating in the light, Arabidopsis (Arabidopsis thaliana) seedlings undergo photomorphogenic development, characterized by short hypocotyls, greening, and expanded cotyledons. Stressed chloroplasts emit retrograde signals to the nucleus that induce developmental responses and repress photomorphogenesis. The nuclear targets of these retrograde signals are not yet fully known. Here, we show that lincomycin-treated seedlings (which lack developed chloroplasts) show strong phenotypic similarities to seedlings treated with ethylene (ET) precursor 1-aminocyclopropane-1-carboxylic acid, as both signals inhibit cotyledon separation in the light. We show that the lincomycin-induced phenotype partly requires a functioning ET signaling pathway, but could not detect increased ET emissions in response to the lincomycin treatment. The two treatments show overlap in upregulated gene transcripts, downstream of transcription factors ETHYLENE INSENSITIVE3 and EIN3-LIKE1. The induction of the ET signaling pathway is triggered by an unknown retrograde signal acting independently of GENOMES UNCOUPLED1. Our data show how two apparently different stress responses converge to optimize photomorphogenesis

Canalización de precursores hacia la biosíntesis de isoprenoides plastídicos en Arabidopsis thaliana

[spa] Los isoprenoides constituyen la familia de metabolitos funcional y estructuralmente más diversa que se conoce. Se encuentran en todos los organismos aunque son especialmente abundantes y diversos en el reino vegetal, donde desempeñan papeles fundamentales en el metabolismo primario y secundario de las plantas. Derivan de un precursor común el isopentenil difosfato (IPP). La condensación de tres moléculas de IPP y una de su isómero dimetilalil difosfato (DMAPP) catalizada por la enzima geranilgeranil difosfato (GGPP) sintasa (GGPPS) genera GGPP, un compuesto precursor de isoprenoides plastídicos como carotenoides, giberelinas, plastoquinonas y la cadena fitol de clorofilas, tocoferoles y filoquinonas. El genoma de Arabidopsis thaliana presenta doce genes codificantes para proteínas con homología a GGPPS, de los cuales sólo diez codifican proteínas con actividad GGPP sintasa. Siete isoformas presentan localización plastídica, dos se encuentran en el retículo endoplasmático y una en la mitocondria. De los genes codificantes, sólo tres presentan un patrón de expresión ubicuo, mientras que el resto se expresan en tejidos y estadios de desarrollo muy concretos. Estos resultados sugieren que diferentes isoformas de GGPPS podrían estar asociadas a la formación de isoprenoides específicos. El primer objetivo de esta tesis fue investigar si en la célula vegetal existe una canalización de precursores (GGPP) hacia la síntesis de grupos concretos de isoprenoides, y en concreto hacia la síntesis de carotenoides. De las 10 isoformas de Arabidopsis, nuestra investigación se ha centrado en la isoforma GGPPS11 por ser la única plastídica de expresión ubicua, alta en tejidos fotosintéticos e inducible por luz, aspectos imprescindibles para estar relacionada con la síntesis de carotenoides. El análisis de tres mutantes de inserción de T-DNA ha revelado que esta isoforma es esencial en la síntesis de isoprenoides y que no presenta redundancia génica con el resto de la familia. La pérdida total de función GGPPS11 es letal y las semillas homocigotas del alelo ggpps11-3 se abortan como consecuencia de un bloqueo en los primeros estadios del desarrollo embrionario. En el mutante ggpps11-2 el T-DNA está insertado en la secuencia codificante del péptido de tránsito a plastos. Hemos demostrado que se traduce una proteína más corta cuya actividad se ejerce fuera del plasto permitiendo el correcto desarrollo embrionario y dando lugar a plántulas albinas incapaces de desarrollar hojas verdaderas como consecuencia de la ausencia de isoprenoides plastídicos. Por último, el mutante ggpps11-4 de pérdida parcial de función presenta un fenotipo de plantas más pequeñas y pálidas con una reducción del 20% en los niveles de carotenoides, clorofilas, tocoferoles y plastoquinonas, lo que permite concluir que esta isoforma está involucrada en la síntesis de la mayoría de los isoprenoides plastídicos derivados del GGPP. Además hemos demostrado que GGPPS11 puede interaccionar con varias enzimas que transforman el GGPP en los primeros intermediarios de las rutas que producen estos isoprenoides plastídicos, las enzimas fitoeno sintasa (PSY) hacia carotenoides, geranilgeranil reductasa (GGR) hacia clorofilas y tocoferoles y solanesil difosfato sintasa (SPPS2) hacia plastoquinonas. Proponemos que estas interacciones estarían facilitando la canalización de GGPP hacia las correspondientes rutas biosintéticas. El segundo objetivo de esta tesis fue analizar la canalización del flujo metabólico hacia la síntesis de carotenoides precursores del ABA en respuesta al estrés salino. Hemos demostrado que el único gen codificante para PSY en Arabidopsis se induce específicamente en la raíz después de un estrés salino para aumentar el flujo hacia la síntesis de carotenoides y que el estrés salino también provoca una inducción de los genes codificantes para las enzimas que sintetizan los precursores carotenoides (β,β-xantofilas) del ácido abscísico (ABA) reconduciendo el flujo de la vía hacia la síntesis de la hormona.[eng] Isoprenoid represent the functionally and structurally most diverse group of metabolites. They are found in all organisms but are especially abundant and diverse in the plant kingdom, which play key roles in the plant primary and secondary metabolism. Most groups of plastidial isoprenoids derive from geranylgeranyl diphosphate (GGPP), which is produced from universal isoprenoid precursors by the enzyme GGPP synthase (GGPPS). In Arabidopsis thaliana, seven active isoforms have been confirmed to localize in plastids, one in the mitochondria and two in the endoplasmatic reticulum. GGPPS11, the most abundant plastidial isoform in vegetative tissues, has been proposed to be the main enzyme producing GGPP in plastids. Our comprehensive analysis of visual, molecular, and metabolic phenotypes of full and partial ggpps11 loss‐of‐function mutants has confirmed this hypothesis and established that GGPPS11 produces GGPP for the major groups of plastidial isoprenoids (carotenoids, chlorophylls, tocopherols, and plastoquinones). We also show that the GGPPS11 protein can physically interact with the enzymes that transform GGPP into the first committed intermediates of the pathways for the production of these plastidial isoprenoid metabolites. We propose that multienzyme complexes containing GGPPS11 and particular GGPP‐consuming enzymes might facilitate the channeling of GGPP to the corresponding isoprenoid biosynthetic pathways. Furthermore, we demonstrate that GGPPS11 might have an extra‐plastidial activity essential for the correct embryo development. As a second objective, we have analyzed the regulation of the carotenoid pathway in response to salt stress. We have demonstrated that the single gene encoding phytoene synthase (PSY), the first committed and flux regulator step or the pathway, in Arabidopsis is specifically induced in the root under salt stress increasing the flow through the synthesis of carotenoids. This stress also leads to the upregulation of other enzymes of the pathway that produce the abscisic acid (ABA) precursors, β,β‐xanthophylls. This root specific transcriptional regulation of the pathway promotes the channeling of carotenoid precursors through the synthesis of the hormone under such stress situation

Investigation of novel components of chloroplast-to-nucleus communication in the unicellular microalgae Chlamydomonas reinhardtii

Resumen del póster presentado al Congreso 'At the Forefront of Plant Research', celebrado en Barcelona (España) del 6 al 8 de mayo de 2019.Besides their well-described role in photosynthesis, chloroplasts act as environmental sensors that are able to regulate nuclear gene expression in response to developmental cues and different stresses. This chloroplast-to-nucleus communication is termed retrograde signaling (RS) and it is a key component in the control of plant growth and development. Despite its essential role, the RS pathway is still poorly understood and many molecular components remain uncharacterized. Most studies on RS have been done in the model plant Arabidopsis thaliana. Here, I present the green unicellular microalga Chlamydomonas reinhardtii as a simpler and advantageous model to address fundamental aspects of RS and find novel RS molecular components. To this end, I will describe the impact of RS in Chlamydomonas physiology and present specific genetic screening strategies and transcriptomic analysis to pinpoint gene regulators of putative positive and negative retrograde signals, and study the crosstalk and timing of light and retrograde control during chloroplast biogenesis, two outstanding questions in the RS field.Peer reviewe

Light-sensitive Phytochrome-Interacting Factors (PIFs) are not required to regulate phytoene synthase gene expression in the root

Carotenoids are plastidial isoprenoids essential for the protection of photosynthetic tissues against excess light. They also serve as precursors of apocarotenoid hormones such as abscisic acid (ABA) and strigolactones. The first enzyme of the carotenoid pathway, phytoene synthase (PSY), is also the main rate-limiting step. Unlike that observed in most plants, PSY is encoded by a single gene in Arabidopsis thaliana. Whereas the PSY gene is induced by light in photosynthetic tissues, a root-specific upregulation of PSY expression by salt stress and ABA has been recently demonstrated. Here we report that transcription factors of the Phytochrome-Interacting Factor (PIF) family, previously shown to repress PSY expression in etiolated seedlings and mature leaves, do not influence PSY expression in roots. Together, our results suggest that organ-specific pathways regulate PSY expression and hence carotenoid production in response to different environmental cues.The work was mainly funded by research grants BIO2011–23680 from the Spanish Dirección General de Investigación (DGI, code BIO2011–23680) and European Union FP7 (TiMet, contract 245143) to M.R.C. DGI also provided funding through a FPI fellowship to M.A.R.S. The Generalitat de Catalunya provided a FI fellowship to A.R.V. and support grants (2009SGR-26 and XRB program). We are members of the IBERCAROT carotenoid network funded by CYTED (code 112RT0445).Peer reviewe

Yellow-in-the-dark mutants: a novel system to study chloroplast biogenesis and retrograde signalling in Chlamydomonas

Trabajo presentado al International Symposium on Plant Photobiology, celebrado virtualmente del 22 al 25 de julio de 2021.Peer reviewe

Light-sensitive Phytochrome-Interacting Factors (PIFs) are not required to regulate phytoene synthase gene expression in the root

Carotenoids are plastidial isoprenoids essential for the protection of photosynthetic tissues against excess light. They also serve as precursors of apocarotenoid hormones such as abscisic acid (ABA) and strigolactones. The first enzyme of the carotenoid pathway, phytoene synthase (PSY), is also the main rate-limiting step. Unlike that observed in most plants, PSY is encoded by a single gene in Arabidopsis thaliana. Whereas the PSY gene is induced by light in photosynthetic tissues, a root-specific upregulation of PSY expression by salt stress and ABA has been recently demonstrated. Here we report that transcription factors of the Phytochrome-Interacting Factor (PIF) family, previously shown to repress PSY expression in etiolated seedlings and mature leaves, do not influence PSY expression in roots. Together, our results suggest that organ-specific pathways regulate PSY expression and hence carotenoid production in response to different environmental cues

Red and blue light differentially impact retrograde signalling and photoprotection in rice

Chloroplast-to-nucleus retrograde signalling (RS) is known to impact plant growth and development. In Arabidopsis, we and others have shown that RS affects seedling establishment by inhibiting deetiolation. In the presence of lincomycin, a chloroplast protein synthesis inhibitor that triggers RS, Arabidopsis light-grown seedlings display partial skotomorphogenesis with undeveloped plastids and closed cotyledons. By contrast, RS in monocotyledonous has been much less studied. Here, we show that emerging rice seedlings exposed to lincomycin do not accumulate chlorophyll but otherwise remain remarkably unaffected. However, by using high red (R) and blue (B) monochromatic lights in combination with lincomycin, we have uncovered a RS inhibition of length and a reduction in the B light-induced declination of the second leaf. Furthermore, we present data showing that seedlings grown in high B and R light display different non-photochemical quenching capacity. Our findings support the view that excess B and R light impact seedling photomorphogenesis differently to photoprotect and optimize the response to high-light stres