title: Pheophytinase Knockdown Impacts Carbon Metabolism and Nutraceutical Content Under Normal Growth Conditions in Tomato.
abstract: Although chlorophyll (Chl) degradation is an essential biochemical pathway for plant physiology, our knowledge regarding this process still has unfilled gaps. Pheophytinase (PPH) was shown to be essential for Chl breakdown in dark-induced senescent leaves. However, the catalyzing enzymes involved in pigment turnover and fruit ripening-associated degreening are still controversial. Chl metabolism is closely linked to the biosynthesis of other isoprenoid-derived compounds, such as carotenoids and tocopherols, which are also components of the photosynthetic machinery. Chls, carotenoids and tocopherols share a common precursor, geranylgeranyl diphosphate, produced by the plastidial methylerythritol 4-phosphate (MEP) pathway. Additionally, the Chl degradation-derived phytol can be incorporated into tocopherol biosynthesis. In this context, tomato turns out to be an interesting model to address isoprenoid-metabolic cross-talk since fruit ripening combines degreening and an intensely active MEP leading to carotenoid accumulation. Here, we investigate the impact of PPH deficiency beyond senescence by the comprehensive phenotyping of SlPPH-knockdown tomato plants. In leaves, photosynthetic parameters indicate altered energy usage of excited Chl. As a mitigatory effect, photosynthesis-associated carotenoids increased while tocopherol content remained constant. Additionally, starch and soluble sugar profiles revealed a distinct pattern of carbon allocation in leaves that suggests enhanced sucrose exportation. The higher levels of carbohydrates in sink organs down-regulated carotenoid biosynthesis. Additionally, the reduction in Chl-derived phytol recycling resulted in decreased tocopherol content in transgenic ripe fruits. Summing up, tocopherol and carotenoid metabolism, together with the antioxidant capacity of the hydrophilic and hydrophobic fractions, were differentially affected in leaves and fruits of the transgenic plants. Thus, in tomato, PPH plays a role beyond senescence-associated Chl degradation that, when compromised, affects isoprenoid and carbon metabolism which ultimately alters the fruit's nutraceutical content.
authors.affiliation: Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Bruno Silvestre
authors.initials: BS
authors.lastname: Lira
authors.affiliation: Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Daniele
authors.initials: D
authors.lastname: Rosado
authors.affiliation: Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Juliana
authors.initials: J
authors.lastname: Almeida
authors.affiliation: Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Amanda Pereira
authors.initials: AP
authors.lastname: de Souza
authors.affiliation: Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Marcos Silveira
authors.initials: MS
authors.lastname: Buckeridge
authors.affiliation: Departamento de Alimentos e Nutrição Experimental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Purgatto
authors.affiliation: Institute of Plant Biology, University of Zurich, Zurich, Switzerland.
authors.forename: Luzia
authors.initials: L
authors.lastname: Guyer
authors.affiliation: Institute of Plant Biology, University of Zurich, Zurich, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hörtensteiner
authors.affiliation: Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Luciano
authors.initials: L
authors.lastname: Freschi
authors.affiliation: Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil mmrossi@usp.br.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Rossi
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000235:genetics; D002244:Carbon / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D002839:Chromans / Q000378:metabolism; D019587:Dietary Supplements / Q000032:analysis*; D055785:Gene Knockdown Techniques; D017343:Genes, Plant; D006867:Hydrolases / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development*; D010788:Photosynthesis; D010802:Phylogeny; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013213:Starch / Q000378:metabolism; D024505:Tocopherols / Q000378:metabolism
chemical_list: D000975:Antioxidants; D002839:Chromans; D012333:RNA, Messenger; D002734:Chlorophyll; D002338:Carotenoids; D002244:Carbon; D013213:Starch; D006867:Hydrolases; D024505:Tocopherols; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid
keywords: Carotenoids; Chlorophyll degradation; Pheophytinase; Solanum lycopersicum; Tocopherol; Tomato