Abstract
BackgroundGenetic manipulation of brassinosteroid (BR) biosynthesis or signaling is a promising strategy to improve crop yield and quality. However, the relationships between the BR-promoted growth and photosynthesis and the exact mechanism of BR-regulated photosynthetic capacity are not clear. Here, we generated transgenic tomato plants by overexpressing Dwarf, a BR biosynthetic gene that encodes the CYP85A1, and compared the photosynthetic capacity with the BR biosynthetic mutant dim and wild type.ResultsOverexpression of Dwarf promoted net photosynthetic rate (PN), whereas BR deficiency in dim led to a significant inhibition in PN as compared with WT. The activation status of RuBisCO, and the protein content and activity of RuBisCO activase, but not the total content and transcripts of RuBisCO were closely related to the endogenous BR levels in different genotypes. However, endogenous BR positively regulated the expression and activity of fructose-1,6-bisphosphatase. Dwarf overexpression enhanced the activity of dehydroascorbate reductase and glutathione reductase, leading to a reduced redox status, whereas BR deficiency had the contrasting effects. In addition, BR induced a reduction of 2-cystein peroxiredoxin without altering the protein content.ConclusionsBR plays a role in the regulation of photosynthesis. BR can increase the photosynthetic capacity by inducing a reduced redox status that maintains the activation states of Calvin cycle enzymes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0715-6) contains supplementary material, which is available to authorized users.
Highlights
Genetic manipulation of brassinosteroid (BR) biosynthesis or signaling is a promising strategy to improve crop yield and quality
BRs promoted CO2 assimilation in tomato plants To examine the role of endogenous BRs in the regulation of photosynthesis, we overexpressed Dwarf gene encoding the CYP85A1 that catalyzes the conversion of 6deoxocastasterone to castasterone in tomato plants and obtained several independent transgenic lines (Fig. 1)
Considering the expression level of the transgene, two lines, DWF:OX2 and DWF:OX3 were selected for further study. qPCR analysis indicated that the expression of Dwarf was enhanced by more than 28 and 17 folds in DWF:OX2 and DWF:OX3, respectively, whereas it was suppressed by c.a. 60 % in the dim mutant as compared to the wild type (WT)
Summary
Genetic manipulation of brassinosteroid (BR) biosynthesis or signaling is a promising strategy to improve crop yield and quality. The relationships between the BR-promoted growth and photosynthesis and the exact mechanism of BR-regulated photosynthetic capacity are not clear. We generated transgenic tomato plants by overexpressing Dwarf, a BR biosynthetic gene that encodes the CYP85A1, and compared the photosynthetic capacity with the BR biosynthetic mutant dim and wild type. Results: Overexpression of Dwarf promoted net photosynthetic rate (PN), whereas BR deficiency in dim led to a significant inhibition in PN as compared with WT. Dwarf overexpression enhanced the activity of dehydroascorbate reductase and glutathione reductase, leading to a reduced redox status, whereas BR deficiency had the contrasting effects. A large body of evidence has shown that photosynthetic capacity is influenced by hormone homeostasis or signaling in plants. Low levels of ethylene promote plant growth [6], whereas ethylene insensitivity results in down-regulation of RuBisCO expression
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