Oral Paper

         Development and Structure

How ectopic cambia form: Insights from the convergent evolution of successive cambia

Presenting Author
Israel Cunha Neto
Description
Among plants, body forms vary from tiny herbs to tall trees. A tree trunk enlarges mostly due to the production of wood and bark. This ability to expand in girth, or radial growth, is an extraordinary feature of plants because wood and inner bark comprises the bulk of vascular tissues. However, in many climbing plants radial growth is different from the typical pattern observed in a sequoia or a pine tree. Instead of forming the typical ring of wood and bark, many stems of climbing species display unusual organizations of vascular tissues which vary from cylindrical stems with heterogeneous distribution of wood and bark to the formation of asymmetrical stems. These anatomies have been hypothesized as adaptations to increased stem flexibility, mechanical support, and water/sugar translocation, contributing to the vine’s ability to climb up on a support. But, how do these complex patterns develop? We aim to answer this question investigating aspects at the gene, tissue, and organismal levels. Towards this aim, we selected a type of radial growth that is very familiar to most people. When you cut open a sugar beet, you will observe concentric rings; this is multiple successively nested vascular cambia within a single root. Technically it is called “successive cambia”. This aberration has evolved independently multiple times across the evolution of vascular plants, therefore presenting a natural experiment to investigate the emergence of de novo meristems from existing plant tissues. Among flowering plants (angiosperms), successive cambia have evolved in several groups, including the Fabaceae or Sapindaceae. In this talk, we focus on the developmental anatomy and molecular genetics underlying de novo meristems which has been investigated in a pair of species of the family Fabaceae; one species has successive cambia (i.e., Wisteria floribunda) and another species has regular anatomy (i.e., common bean, Phaseolus vulgaris). This research will generate the first comparative study of gene expression characterizing successive cambia development. In addition, we investigate processes in molecular evolution across the convergent evolution of successive cambia by testing for signatures of selection, gene duplication, and pseudogenization of conserved vascular genes in a phylogenetic context of species with and without ectopic cambia to reveal the molecular processes shaping their evolution across plants. Together these data will reveal which gene expression patterns are shared across lineages, and which gene expression patterns are specific to generating successive cambia within a lineage. Therefore, this research will shed light on how successive cambia form across vascular plants, which at the same time can illuminate how radial growth occur in ecological and economic important commercial trees.