Células del mesófilo de plantas de arabidopsis que no poseen fosfoglucoisomerasa plastidial acumulan almidón

Está generalmente admitido que todo el proceso de biosíntesis del almidón que tiene lugar en las células del mesófilo de la hoja reside exclusivamente en el cloroplasto. Según esta interpretación el almidón transitorio es el producto final de una ruta metabólica en la que participan las enzimas fosfoglucomutasa plastidial (pPGM), ADPglucosa pirofosforilasa (AGP) y almidón sintasa (SS) que estaría conectada con el ciclo de Calvin-Benson a través de de la fosfoglucosa isomerasa plastidial (pPGI). Sin embargo, estudios llevados a cabo en el grupo “Metabolismo de Carbohidratos” del Instituto de Agrobiotecnología de Navarra han demostrado que hojas del mutante pgi1-2 sin actividad pPGI (a) acumulan en las células del mesófilo un 10% del almidón que poseen las hojas de una planta salvaje (WT), (b) poseen niveles WT de la molécula precursora del almidón, el ADP-glucosa, y (c) poseen una reducida capacidad fotosintética y una elevada actividad degradadora de almidón. En este trabajo nos planteamos producir y caracterizar un doble mutante pgi1-2/sex1 incapaz de degradar almidón. El rationale de esta aproximación experimental es que si el mutante pgi1-2 es capaz de acumular almidón en las células del mesófilo, las hojas del doble mutante pgi1-2/sex1 deberían acumular más almidón que las hojas pgi1-2, dado que el alelo sex1 impide que se degrade el almidón. Los resultados obtenidos en este trabajo (a) apoyan aún más la idea de que las células del mesófilo del mutante pgi1-2 acumulan almidón, y (b) soportan la existencia de importantes vía(s) alternativa(s) de síntesis de almidón diferentes a la vía clásica.It is widely assumed that the whole starch biosynthetic process occurring in leaf mesophyll cells resides exclusively in the chloroplast. According to this view, the transitory starch is considered the end product of a metabolic pathway involving in the plastid phosphoglucomutase enzymes (pPGM), ADP-glucose pyrophosphorylase (AGP) and starch synthase (SS) that is linked to the Calvin-Benson cycle by means of the plastid phosphoglucose isomerase (pPGI). The pgi1-2 mutant is a null mutant of pPGI by insertion of a T-DNA. Given that (a) leaves of this mutant have 10% of WT starch, (b) starch is accumulated in mesophyll cells, and (c) pgi1-2 possesses WT levels of the starch precursor molecule, ADP- glucose, in this work I carried out the characterization of the pgi1-2/sex1 double mutant. The rationale behind this experimental approach was that, if pgi1-2 mesophyll cells do indeed accumulate starch, pgi1-2/sex1 leaves should accumulated more starch than pgi1-2, since sex1 mutation impedes -amylase-mediated starch breakdown. The overall data (a) showed that mesophyll cells of pPGI null mutants are able to accumulate starch, and (b) supported the occurrence of important starch biosynthetic pathway (s) alternative (s) to the classic pathway.Máster Universitario en AgrobiotecnologíaUnibertsitate Masterra Agrobioteknologia

Vascular and root tip GPT2 expression mediates the PGI1-independent response of Arabidopsis to small microbial volatiles

Resumen del trabajo presentado en el XVI Meeting of Plant Molecular Biology, celebrado en Sevilla (España), del 14 al 16 de septiembre de 2022Microorganisms emit a plethora of volatile compounds (VCs) that promote plant growth and photosynthesis as well as strong developmental and metabolic changes. In Arabidopsis, the plastidial isoform of phosphoglucose isomerase PGI1 mediates photosynthesis, metabolism and development, probably due to its involvement in the synthesis of isoprenoid-derived signals in vascular tissues (Bahaji et al., 2015; Bahaji et al., 2018). Like in wild-type (WT) plants, microbial VCs promote growth and photosynthesis as well as starch and CK accumulation in PGI1-lacking pgi1-2 plants (Sánchez-López et al. 2016). A striking alteration in the transcriptome of leaves of small fungal VC-treated plants involves strong up-regulation of levels of transcripts of GPT2 (At1g61800), a gene that codes for a plastidial G6P/Pi transporter. We hypothesized that the PGI1-independent response to microbial volatile emissions involves GPT2 action. To test this hypothesis, we characterized responses of WT, GPT2-null gpt2-1, PGI1-null pgi1-2 and pgi1- 2gpt2-1 plants to small fungal VCs. In addition, we characterized responses of pgi1-2gpt2-1 plants expressing GPT2 under the control of a vascular tissue- and root tip-specific promoter to small fungal VCs. Results presented in this work provide evidence that, under conditions in which PGI1 activity is reduced, long-distance action of GPT2 plays an important role in the response of plants to small VCs through mechanisms involving resetting of the photosynthesis-related proteome in leaves and complex GPT2 regulation.This work was supported by the Ministerio de Ciencia e Innovación (MCIN) and Agencia Estatal de Investigación (AEI) / 10.13039/501100011033/ (grants BIO2016-78747-P, PID2019-104685GB-100 and PID2019-107657RB-C22) and the Ministry of Education, Youth and Sport of the Czech Republic and ERDF project entitled “Plants as a tool for sustainable global development” (No. CZ.02.1.01/0.0/0.0/16_019/0000827)