Reprogramming of gene expression during compression wood formation in pine: coordinated modulation of S-adenosylmethionine, lignin and lignan related genes

Transcript profiling of differentiating secondary xylem has allowed us to draw a generalpicture of the genes involved in wood formation. However, our knowledge is still limitedabout the regulatory mechanisms that coordinate and modulate the different pathwaysproviding substrates during xylogenesis.

The development of compression wood in conifersconstitutes an exceptional model for these studies. Although differential expression of a fewgenes in differentiating compression wood compared to normal or opposite wood has beenreported, the broad range of features that distinguish this reaction wood suggest that theexpression of a larger set of genes would be modified.

Results: By combining the construction of different cDNA libraries with microarray analyses we haveidentified a total of 496 genes in maritime pine (Pinus pinaster, Ait.) that change inexpression during differentiation of compression wood (331 up-regulated and 165 downregulatedcompared to opposite wood).

Samples from different provenances collected indifferent years and geographic locations were integrated into the analyses to mitigate theeffects of multiple sources of variability. This strategy allowed us to define a group of genesthat are consistently associated with compression wood formation.

Correlating with thedeposition of a thicker secondary cell wall that characterizes compression wood development,the expression of a number of genes involved in synthesis of cellulose, hemicellulose, ligninand lignans was up-regulated. Further analysis of a set of these genes involved in Sadenosylmethioninemetabolism, ammonium recycling, and lignin and lignans biosynthesisshowed changes in expression levels in parallel to the levels of lignin accumulation in cellsundergoing xylogenesis in vivo and in vitro.

Conclusions: The comparative transcriptomic analysis reported here have revealed a broad spectrum ofcoordinated transcriptional modulation of genes involved in biosynthesis of different cell wallpolymers associated with within-tree variations in pine wood structure and composition.

Inparticular, we demonstrate the coordinated modulation at transcriptional level of a gene setinvolved in S-adenosylmethionine synthesis and ammonium assimilation with increased demand for coniferyl alcohol for lignin and lignan synthesis, enabling a better understandingof the metabolic requirement in cells undergoing lignification.

Published on: 2012-06-29

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