Identifying Genes That Regulate Secondary Growth In Poplar

Abstract

Plant growth and development is largely controlled in regions of totipotential cells around the plant body called meristems. The well characterized shoot and root apical meristems are responsible for vertical growth, in which many key players have been well studied. Lateral (secondary) growth is controlled by the vascular and cork cambiums, which are much less understood. A rapid growth of interest in a new model angiosperm tree, poplar, has facilitated the study of the two cambiums, specifically into their regulation at the genomic and proteomic levels. This study describes recent work carried out to explore the genetic regulation of secondary growth in poplar. Two genes have been identified that were previously not associated with the process of secondary growth. The first, a gene lacking annotation (FM#2), was identified through the investigation of a mutant from an activation-tagged population of poplar. This mutant showed aberrant secondary growth, with an increase in the phloem:xylem ratio. It also developed a thick, rough bark, and was subsequently named corky. Constructs to recapitulate this phenotype have been produced to allow the link between the gene FM#2 and the corky phenotype to be firmly established. The second gene was identified through a reverse genetics strategy to test if the Arabidopsis shoot apical meristem regulator, CLAVATA1 also played a role in the regulation of the vascular cambium. When it was downregulated in Arabidopsis, a significant increase in secondary growth was observed. Antisense and hairpin-RNAi constructs were produced to attempt downregulation of the gene in poplar using both traditional Agrobacterium-mediated transformations, and the recently developed strategy of induced somatic sector analysis.