Format: ORAL

Israel L. Cunha Neto, Anthony Snead2, Jacob B. Landis3, Chelsea D. Specht3, and Joyce G. Onyenedum

1 Department of Environmental Studies, New York University, New York, USA 2 Department of Biology, New York University, New York, USA 3 Section of Plant Biology and the L.H. Bailey Hortorium, Cornell University, Ithaca, USA

Secondary growth is a remarkable evolutionary innovation in vascular plants, representing a developmental process through which plants increase in thickness. Typically, secondary growth generates a core secondary xylem (wood) surrounded by a sheath of secondary phloem (inner bark), and this pattern is achieved through a delicate balance between cell initiation, proliferation, differentiation, and programmed cell death all governed by a single stem-cell region called the vascular cambium. Thousands of seed plants share this conserved mode of radial growth, which is regulated by a common set of conserved genes. However, this typical modality of vascular radial growth has been disrupted in several lineages of gymnosperms and angiosperms that contain alternative vascular developmental pathways called vascular variants. In certain lineages, the presence of vascular variants becomes especially intriguing when the stem produces supplementary vascular cambia in unconventional locations, in addition to the initially formed original vascular cambium. This phenomenon is called ectopic cambia and generates distinct anatomical patterns, most commonly successive cambia where concentric rings of cambium and its products encircle the stem/root. This process results in the development of stems or roots with multiple cambia. In this study, we investigate the evolution and development of ectopic cambia, with a particular focus on the Fabaceae. By comparing Phaseolus vulgaris (typical secondary growth) to Wisteria floribunda (ectopic cambia), we combine anatomy with comparative transcriptomes to elucidate the developmental and molecular mechanisms underlying successive cambia formation. We generated seventeen transcriptomes to explore variations in gene expression within and between species, focusing on both typical and ectopic cambia. Moreover, we explore the molecular evolution of conserved genes related to vascular development (WOX4, CLE41, PXY, ER) to test for signatures of selection, gene duplication, and pseudogenization in lineages with and without successive cambia.