Research article

A multi-treatment experimental system to examine photosynthetic differentiation in the maize leaf

Ruairidh JH Sawers^1,4 , Peng Liu^2,5 , Katya Anufrikova¹ , JT Gene Hwang^2,3 and Thomas P Brutnell¹

¹  Boyce Thompson Institute, Cornell University, Tower Road, Ithaca, NY 14853, USA

²  Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, NY 14853, USA

³  Department of Mathematics and Department of Statistics, Cornell University, Ithaca, NY 14853, USA

⁴  Department of Plant Molecular Biology, Biophore, University of Lausanne, CH-1015 Lausanne, Switzerland

⁵  Department of Statistics, Iowa State University, Ames IA 50011, USA

author email corresponding author email

BMC Genomics 2007, 8:12doi:10.1186/1471-2164-8-12

Published:	9 January 2007

Abstract

Background

The establishment of C₄ photosynthesis in maize is associated with differential accumulation of gene transcripts and proteins between bundle sheath and mesophyll photosynthetic cell types. We have physically separated photosynthetic cell types in the leaf blade to characterize differences in gene expression by microarray analysis. Additional control treatments were used to account for transcriptional changes induced by cell preparation treatments. To analyse these data, we have developed a statistical model to compare gene expression values derived from multiple, partially confounded, treatment groups.

Results

Differential gene expression in the leaves of wild-type maize seedlings was characterized using the latest release of a maize long-oligonucleotide microarray produced by the Maize Array Project consortium. The complete data set is available through the project web site. Data is also available at the NCBI GEO website, series record GSE3890. Data was analysed with and without consideration of cell preparation associated stress.

Conclusion

Empirical comparison of the two analyses suggested that consideration of stress helped to reduce the false identification of stress responsive transcripts as cell-type enriched. Using our model including a stress term, we identified 8% of features as differentially expressed between bundle sheath and mesophyll cell types under control of false discovery rate of 5%. An estimate of the overall proportion of differentially accumulating transcripts (1-π₀) suggested that as many as 18% of the genes may be differentially expressed between B and M. The analytical model presented here is generally applicable to gene expression data and demonstrates the use of statistical elimination of confounding effects such as stress in the context of microarray analysis. We discuss the implications of the high degree of differential transcript accumulation observed with regard to both the establishment and engineering of the C₄ syndrome.