Mutation of Arabidopsis Plastid Phosphoglucose Isomerase Affects Leaf Starch Synthesis and Floral Initiation

Abstract

We isolated pgi1-1, an Arabidopsis mutant with a decreased plastid phospho-glucose (Glc) isomerase activity. While pgi1-1 mutant has a deficiency in leaf starch synthesis, it accumulates starch in root cap cells. It has been shown that a plastid transporter for hexose phosphate transports cytosolic Glc-6-P into plastids and expresses restricted mainly to the heterotrophic tissues. The decreased starch content in leaves of the pgi1-1 mutant indicates that cytosolic Glc-6-P cannot be efficiently transported into chloroplasts to complement the mutant's deficiency in chloroplastic phospho-Glc isomerase activity for starch synthesis. We cloned the Arabidopsis PGI1 gene and showed that it encodes the plastid phospho-Glc isomerase. The pgi1-1 allele was found to have a single nucleotide substitution, causing a Ser to Phe transition. While the flowering times of the Arabidopsis starch-deficient mutants pgi1, pgm1, and adg1 were similar to that of the wild type under long-day conditions, it was significantly delayed under short-day conditions. The pleiotropic phenotype of late flowering conferred by these starch metabolic mutations suggests that carbohydrate metabolism plays an important role in floral initiation.Most plants synthesize starch in their chloroplasts during photosynthesis and degrade it during the subsequent night. The regulation of transitory starch metabolism in photosynthetic tissues is clearly different from the long-term, reserve starch metabolism in non-photosynthetic tissues (Caspar, 1994). Many mutations that affect the starch of certain cereal seeds, potato, pea, and Chlamydomonas reinhardtii have been isolated and characterized (Hannah, 1997). Although studies of these mutants have greatly added to our knowledge of starch metabolism, these mutants studied are relatively specific for the reserve and reproductive organs, and do not affect starch metabolism in the vegetative parts of plants. Mutants that affect starch metabolism in the vegetative parts of Arabidopsis would be useful to extend our understanding on starch metabolism and its role in the plant.Previously, several nuclear-encoded, recessive mutants of Arabidopsis, pgm1, adg1, and adg2, were isolated and characterized for their low starch content or lack of starch in leaves (Caspar et al

Isolation and Characterization of Mutants of Common Ice Plant Deficient in Crassulacean Acid Metabolism

“…The slow-growth phenotype is similar to that observed for the starchless mutant of Arabidopsis deficient in chloroplast PGM activity also grown under a 12-h photoperiod (Caspar et al, 1985), but not for the starchless mutant of N. sylvestris defective in plastid PGM grown under a 16-h light photoperiod (Hanson and McHale, 1988). Floral initiation can be delayed and seed production reduced by up to 50% in starch-deficient mutants of Arabidopsis (Schulze et al, 1994;Yu et al, 2000). However, the 90% reduction in seed number from line 351 greatly exceeded that predicted just from starch deficiency alone and is comparable to the reduction in reproductive output reported when common ice plants were deprived of CO 2 each night to minimize nocturnal carbon gain (Winter and Ziegler, 1992).…”

Orchestration of Thiamin Biosynthesis and Central Metabolism by Combined Action of the Thiamin Pyrophosphate Riboswitch and the Circadian Clock in Arabidopsis

“…Similarly, riboswitchdeficient plants displayed delayed flowering only under short-day conditions. This might result from alteration in their circadian clock (Imaizumi and Kay, 2006) or alternatively from perturbation in carbohydrate metabolism (Bernier et al, 1993;Levy and Dean, 1998;Yu et al, 2000). Given that the circadian clock of the riboswitch-deficient plants was not affected (illustrated by oscillations of GRP7), the aberrant starch metabolism of the riboswitch-deficient plants was likely the cause of the flowering retardation phenotype.…”

SUGAR-DEPENDENT6 Encodes a Mitochondrial Flavin Adenine Dinucleotide-Dependent Glycerol-3-P Dehydrogenase, Which Is Required for Glycerol Catabolism and Postgerminative Seedling Growth in Arabidopsis

“…Arabidopsis contains a cytosolic and a plastidial isozyme of PGI, whose activities can be discriminated based on their different temperature stability (Yu et al, 2000). Assays performed on extracts from seedlings show that approximately 60% of the activity is present in the cytosol and that there is no significant difference in total activity between the wild type and sdp6-1 (Table III).…”

“…The inhibitory effect of G3P was tested by adding 2 to 20 mM to the reaction buffer. Plastidial PGI was inactivated by heating the extract at 50°C for 10 min (Yu et al, 2000).…”