title: Plastidic phosphoglucose isomerase is an important determinant of starch accumulation in mesophyll cells, growth, photosynthetic capacity, and biosynthesis of plastidic cytokinins in Arabidopsis.
abstract: Phosphoglucose isomerase (PGI) catalyzes the reversible isomerization of glucose-6-phosphate and fructose-6-phosphate. It is involved in glycolysis and in the regeneration of glucose-6-P molecules in the oxidative pentose phosphate pathway (OPPP). In chloroplasts of illuminated mesophyll cells PGI also connects the Calvin-Benson cycle with the starch biosynthetic pathway. In this work we isolated pgi1-3, a mutant totally lacking pPGI activity as a consequence of aberrant intron splicing of the pPGI encoding gene, PGI1. Starch content in pgi1-3 source leaves was ca. 10-15% of that of wild type (WT) leaves, which was similar to that of leaves of pgi1-2, a T-DNA insertion pPGI null mutant. Starch deficiency of pgi1 leaves could be reverted by the introduction of a sex1 null mutation impeding β-amylolytic starch breakdown. Although previous studies showed that starch granules of pgi1-2 leaves are restricted to both bundle sheath cells adjacent to the mesophyll and stomata guard cells, microscopy analyses carried out in this work revealed the presence of starch granules in the chloroplasts of pgi1-2 and pgi1-3 mesophyll cells. RT-PCR analyses showed high expression levels of plastidic and extra-plastidic β-amylase encoding genes in pgi1 leaves, which was accompanied by increased β-amylase activity. Both pgi1-2 and pgi1-3 mutants displayed slow growth and reduced photosynthetic capacity phenotypes even under continuous light conditions. Metabolic analyses revealed that the adenylate energy charge and the NAD(P)H/NAD(P) ratios in pgi1 leaves were lower than those of WT leaves. These analyses also revealed that the content of plastidic 2-C-methyl-D-erythritol 4-phosphate (MEP)-pathway derived cytokinins (CKs) in pgi1 leaves were exceedingly lower than in WT leaves. Noteworthy, exogenous application of CKs largely reverted the low starch content phenotype of pgi1 leaves. The overall data show that pPGI is an important determinant of photosynthesis, energy status, growth and starch accumulation in mesophyll cells likely as a consequence of its involvement in the production of OPPP/glycolysis intermediates necessary for the synthesis of plastidic MEP-pathway derived hormones such as CKs.
authors: Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, Mutiloabeti, Nafarroa, 31192, Spain.
authors: Abdellatif
authors: A
authors: Bahaji
authors: Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, Mutiloabeti, Nafarroa, 31192, Spain.
authors: Ángela M
authors: ÁM
authors: Sánchez-López
authors: Department of Chemical Biology and Genetics, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University, Olomouc, CZ-78371, Czech Republic.
authors: Nuria
authors: N
authors: De Diego
authors: Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, Mutiloabeti, Nafarroa, 31192, Spain.
authors: Francisco J
authors: FJ
authors: Muñoz
authors: Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, Mutiloabeti, Nafarroa, 31192, Spain.
authors: Edurne
authors: E
authors: Baroja-Fernández
authors: Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, Mutiloabeti, Nafarroa, 31192, Spain.
authors: Jun
authors: J
authors: Li
authors: Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, Mutiloabeti, Nafarroa, 31192, Spain.
authors: Adriana
authors: A
authors: Ricarte-Bermejo
authors: Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, Mutiloabeti, Nafarroa, 31192, Spain.
authors: Marouane
authors: M
authors: Baslam
authors: Plant Biology and Ecology Department, Science and Technology Faculty, University of the Basque Country, Barrio Sarriena, 48940 Leioa, Spain.
authors: Iker
authors: I
authors: Aranjuelo
authors: Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, Mutiloabeti, Nafarroa, 31192, Spain.
authors: Goizeder
authors: G
authors: Almagro
authors: Department of Chemical Biology and Genetics, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University, Olomouc, CZ-78371, Czech Republic.
authors: Jan F
authors: JF
authors: Humplík
authors: Laboratory of Growth Regulators, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University and Institute of Experimental Botany ASCR, Olomouc, CZ-78371, Czech Republic.
authors: Ondřej
authors: O
authors: Novák
authors: Plant Biology and Ecology Department, Science and Technology Faculty, University of the Basque Country, Barrio Sarriena, 48940 Leioa, Spain.
authors: Lukáš
authors: L
authors: Spíchal
authors: Plant Biology and Ecology Department, Science and Technology Faculty, University of the Basque Country, Barrio Sarriena, 48940 Leioa, Spain.
authors: Karel
authors: K
authors: Doležal
authors: Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, Mutiloabeti, Nafarroa, 31192, Spain.
authors: Javier
authors: J
authors: Pozueta-Romero
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D003583:Cytokinins / Q000378:metabolism*; D004896:Erythritol / Q000031:analogs & derivatives / Q000378:metabolism; D056426:Genetic Loci; D005956:Glucose-6-Phosphate Isomerase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D058503:Mesophyll Cells / Q000378:metabolism*; D053858:Metabolic Networks and Pathways; D009154:Mutation; D010641:Phenotype; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism; D013213:Starch / Q000378:metabolism*; D013403:Sugar Phosphates / Q000378:metabolism
chemical_list: C114232:2-C-methylerythritol 4-phosphate; D029681:Arabidopsis Proteins; D003583:Cytokinins; D013403:Sugar Phosphates; D013213:Starch; D005956:Glucose-6-Phosphate Isomerase; D004896:Erythritol