Genetic suppression analysis in novel vacuolar processing enzymes reveals their roles in controlling sugar accumulation in tomato fruits

• Published in: Journal of experimental botany Vol. 62; no. 8; pp. 2773 - 2786
• Main Authors: Ariizumi, Tohru, Higuchi, Kenji, Arakaki, Shoko, Sano, Tsunenori, Asamizu, Erika, Ezura, Hiroshi
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.05.2011
• Subjects: amino acid composition; Amino Acids; Amino Acids - metabolism; Biological and medical sciences; Carbohydrate Metabolism; Carbohydrate Metabolism - genetics; Cysteine Endopeptidases; Cysteine Endopeptidases - genetics; Cysteine Endopeptidases - metabolism; cysteine proteinases; endoplasmic reticulum; enzyme activity; Enzymes; enzymology; Fruit; Fruit - enzymology; Fruit - genetics; Fruit - growth & development; Fruiting; Fruits; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; genes; Genes, Reporter; genetic techniques and protocols; genetics; Glucuronidase; Glucuronidase - metabolism; growth & development; Immunohistochemistry; Lycopersicon esculentum; Lycopersicon esculentum - enzymology; Lycopersicon esculentum - genetics; Lycopersicon esculentum - growth & development; Messenger RNA; metabolism; Phylogeny; Plant physiology and development; Plant Proteins; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Plants, Genetically Modified; post-translational modification; Proteins; quantitative analysis; RESEARCH PAPER; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; RNA, Messenger; RNA, Messenger - genetics; RNA, Messenger - metabolism; Seeds; Solanum; Solanum lycopersicum; sugar content; Sugars; Suppression, Genetic; testa; Time Factors; tomatoes; Vacuoles; RNA interference; Fruit; Enzyme; Fruit vegetable; Tomato; Vacuole; sugar accumulation; Genetic determinism; Gene silencing; Vegetable crop; Dicotyledones; Angiospermae; Botany; Lycopersicon esculentum; vacuolar processing enzyme; Spermatophyta; Solanaceae; Sugar
• ISSN: 0022-0957; 1460-2431; 1460-2431
• DOI: 10.1093/jxb/erq451

In plant cells, many vacuolar proteins are synthesized as precursors in the endoplasmic reticulum and are subsequently transported to the vacuole. These precursors are subject to post-translational modifications to allow the active mature forms to be produced. Vacuolar processing enzyme (VPE) has been identified as a family of cysteine proteases involved in protein maturation in the vacuole. In this study, novel VPE genes were isolated from tomato (Solanum lycopersicum), and they were designated SIVPE1–SIVPE5. Phylogenic analysis suggested that SIVPE1 and SIVPE2 were categorized as the seed coat type, SIVPE4 was categorized as the seed type, and both SIVPE3 and SIVPE5 were categorized as the vegetative type. Expression analysis demonstrated that these genes were expressed during fruit development, and that their expression profiles agreed with this classification. High VPE enzyme activity was observed during tomato fruit development; the enzyme activity was correlated with the SIVPE mRNA levels, indicating that the SIVPE encoded active VPE proteins. The total sugar content was higher in RNA interference (RNAi) lines compared with the control plants, suggesting negative roles for SIVPE in sugar accumulation. The quantitative expression analysis of each SIVPE gene in the RNAi lines suggested that the suppression of SIVPE5 probably had the strongest effect on the sugar accumulation observed. The suppression of SIVPE did not influence the total amino acid content, suggesting that the molecular targets of SIVPE were mainly involved in sugar accumulation.