Point Mutation of a Plastidic Invertase Inhibits Development of the Photosynthetic Apparatus and Enhances Nitrate Assimilation in Sugar-treated Arabidopsis Seedlings

Abstract

Because the photosynthetic apparatus contains a massive amount of nitrogen in plants, the regulation of its development by sugar signals is important to the maintenance of the carbonnitrogen balance. In this study we isolated an Arabidopsis mutant (sicy-192) whose cotyledon greening was inhibited by treatments with sugars such as sucrose, glucose, and fructose. In the mutant, the gene encoding plastidic alkaline/neutral invertase (INV-E) was point-mutated at codon 294, with Tyr substituted for Cys (C294Y). Interestingly, the greening of cotyledons in the knock-out INV-E lines was not inhibited by treatment with the sugars. In addition, the knock-out INV-E lines expressing an INV-E:C294Y or INV-E:C294A gene had the same phenotype as sicy-192 mutants, whereas the lines expressing a wildtype INV-E gene had the same phenotype as wild-type plants. A recombinant INV-E:C294Y protein had the same enzymatic activity as a recombinant INV-E protein, suggesting that the Cys-294 residue of INV-E is important for its functions in the chloroplasts. On treatment with sucrose, the expression of photosynthesis-related genes was weaker in seedlings of mutant plants than wild-type seedlings, whereas the activity of nitrate reductase was stronger in the mutant plants than wild-type plants. These findings suggest that Cys-294 of INV-E is associated with the development of the photosynthetic apparatus and the assimilation of nitrogen in Arabidopsis seedlings to control the ratio of sucrose content to hexose content.

A Transcriptomic Network Underlies Microstructural and Physiological Responses to Cadmium in Populus × canescens

“…In cadmium-exposed Populus tremula leaves, repression of essential proteins involved in the photosystem, chlorophyll biosynthesis, and carbohydrate metabolism has been detected (Kieffer et al, 2008(Kieffer et al, , 2009b. Because chloroplast-targeted alkaline/neutral invertase and chloroplastidic phosphoglucanase are involved in hydrolysis of Suc and starch, respectively (Hejazi et al, 2008;Tamoi et al, 2010), activation of both genes is in line with the changes in Suc and starch that we observed in the bark of cadmium-treated P. 3 canescens. In addition, decreased transcript levels of galactinol synthase1 and raffinose synthase5 may have contributed to the reductions in inositol and mannitol concentrations in the P. 3 canescens bark because both genes are involved in inositol and mannitol metabolism (Zuther et al, 2004;Nishizawa et al, 2008).…”

New insights into the regulation of greening and carbon-nitrogen balance by sugar metabolism through a plastidic invertase

“…1 Therefore, previous reports and our findings suggest that sugar metabolism through INV-E in plastids is associated with PGE and plastid signaling.…”

“…However, ABA had no effect on the greening of sicy-192 mutants grown in the Suc + medium (data not shown). Moreover, the sicy-192 and abi4 (abscisic acid insensitive 4) double mutants, in which the transcription factor ABI4 involved in ABA signaling as well as sugar and plastid signaling is disrupted, 6 showed the same sugar-sensitivity as the sicy-192 mutants, 1 indicating that the greening inhibition in sicy-192 mutants was ABA-independent. Interestingly, co-treatment with sucrose and 1-amino cyclopropane-1-carbonic acid (ACC), a precursor of ethylene, markedly enhanced the greening inhibition in sicy-192 mutants compared to sucrose alone (Fig.…”

“…The system for regulating the distribution of nitrogen via sugar signaling appears to be important for the adjustment of primary metabolism to ensure growth, survival and completion of the life cycle in plants. Therefore, the New insights into the regulation of greening and carbon-nitrogen balance by sugar metabolism through a plastidic invertase 1 On treatment with sucrose, the expression of photosynthesis-related genes was weaker in the mutant than wild-type seedlings, while the activity of nitrate reductase was stronger in the mutant. In the sicy-192 plants, the gene encoding plastidic alkaline/neutral (A/N) invertase (INV-E) was point-mutated at codon 294, with Tyr substituted for Cys (C294Y), but a recombinant INV-E:C294Y protein had the same enzymatic activity and substrate specificity as a recombinant INV-E protein.…”

“…These findings provide new insights into the regulation of greening and carbonnitrogen balance by sugar metabolism through INV-E in plastids. 1 In this addendum, we describe the effects of treatment with sucrose and plant hormones on the greening of sicy-192 mutants in detail, and discuss how INV-E is involved in the regulation of plant development and metabolism.…”