Induction of PrMADS10 on the lower side of bent pine tree stems: potential role in modifying plant cell wall properties and wood anatomy

The molecular mechanisms underlying inclination responses in trees are unclear. In this study, we identified a MADS-box transcription factor differentially expressed early after inclination in the stems of Pinus radiata D. Don. PrMADS10 has a CDS of 582 bp and encodes a group II MADS-box transcription factor. We measured highest accumulation of this transcript on the lower side of inclined pine stems. In an effort to identify putative targets, we stably transformed Arabidopsis thaliana with a 35S::PrMADS10 construct. Transcriptome analysis revealed 1,219 genes differentially-expressed, with 690 and 529 genes up- and down-regulated respectively, when comparing the transgenic and wild-type. Differentially-expressed genes belong to different biological processes, but were enriched in cell wall remodeling and phenylpropanoid metabolic functions. Interestingly, lignin content was 30% higher in transgenic as compared to wild-type plants consistent with observed changes in gene expression. Differentially expressed transcription factors and phenylpropanoid genes were analyzed using STRING. Several MYB and NAC transcription factors showed interactions with genes of the phenylpropanoid pathway. Together, these results implicate PrMADS10 as a regulatory factor, triggering the expression of other transcription factors and genes involved in the synthesis of lignin.