Abstract
Histone modifications play important roles in regulating the expression of C4 photosynthetic genes. Given that all enzymes required for the C4 photosynthesis pathway are present in C3 plants, it has been hypothesized that this expression regulatory mechanism has been conserved. However, the relationship between histone modification and the expression of homologs of C4 photosynthetic enzyme genes has not been well determined in C3 plants. In the present study, we cloned nine hybrid poplar (Populus simonii × Populus nigra) homologs of maize (Zea mays) C4 photosynthetic enzyme genes, carbonic anhydrase (CA), pyruvate orthophosphate dikinase (PPDK), phosphoenolpyruvate carboxykinase (PCK), and phosphoenolpyruvate carboxylase (PEPC), and investigated the correlation between the expression levels of these genes and the levels of promoter histone acetylation modifications in four vegetative tissues. We found that poplar homologs of C4 homologous genes had tissue-dependent expression patterns that were mostly well-correlated with the level of histone acetylation modification (H3K9ac and H4K5ac) determined by chromatin immunoprecipitation assays. Treatment with the histone deacetylase inhibitor trichostatin A further confirmed the role of histone acetylation in the regulation of the nine target genes. Collectively, these results suggest that both H3K9ac and H4K5ac positively regulate the tissue-dependent expression pattern of the PsnCAs, PsnPPDKs, PsnPCKs, and PsnPEPCs genes and that this regulatory mechanism seems to be conserved among the C3 and C4 species. Our findings provide new insight that will aid efforts to modify the expression pattern of these homologs of C4 genes to engineer C4 plants from C3 plants.
Highlights
The C3 photosynthetic pathway is the predominant method of carbon fixation and is used by over 90% of terrestrial plant species
We used the known protein sequences of maize C4-carbonic anhydrase (CA) (GRMZM2G121878), C4-pyruvate orthophosphate dikinase (PPDK) (GRMZM2G306345), C4-phosphoenolpyruvate carboxykinase (PCK) (GRMZM2G001696), and C4-phosphoenolpyruvate carboxylase (PEPC) (GRMZM2G083841) as queries to blast against the P. trichocarpa genome database1
Analysis of genome sequences for a growing number of species has indicated that all of the enzymes required for C4 photosynthesis are present in C3 plants, and even in algae and microorganisms
Summary
The C3 photosynthetic pathway is the predominant method of carbon fixation and is used by over 90% of terrestrial plant species. C3 photosynthesis is relatively inefficient, due to the inefficiency of the carbon-fixing enzyme, Rubisco, which catalyzes both carboxylation (carbon fixation) and oxygenation (photorespiration). The light dependent reactions and the first carbon fixation step occur in the mesophyll cells, whereas the second carbon fixation step by Rubisco occurs in the lower oxygen environment of the bundle sheath cells. In addition to altered anatomical structures, the evolution of C4 photosynthesis required changes in the expression of essential enzymes such as PEPC and CA that catalyze the CO2 concentration reactions, and PPDK, NADP- or NAD-dependent malic enzymes (NADPME or NAD-ME, respectively) and PCK that shuttle four-carbon acids between the mesophyll and bundle sheath cells (Hatch et al, 1975)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
