Epsilon Archive for Student Projects

Abstract

When plant tissues are wounded the most important action for the plant’s survival is to heal the vascular strands to resume transport of water and nutrients. In addition to wound healing, the agricultural and horticultural practice of grafting, the joining of plant tissues from two individuals to form one, also requires the reconnection of vasculature over the graft junction. Similarities between regeneration and grafting have been found with leaf vein formation and hijacking of vasculature in parasitic interactions. Common traits in vascular formation are the activation of, or dedifferentiation to, cambium and the differentiation to xylem and phloem. Recently, RNAseq data from hypocotyl grafts in Arabidopsis thaliana showed considerable expression upregulation of members in the gene family PECTATE LYASE-LIKE (PLL) which encodes pectate lyases, enzymes involved in pectin degradation. Pectin is one of the main components of the cell wall and the middle lamella between plant cells. Cell wall degrading enzymes contribute to cell wall loosening and cell separation which is required for division, expansion and elongation of cells. The transcriptomics data points to the involvement of five PLL genes in vascular reconnection during grafting. However, their role in vascular differentiation and regeneration have not been further investigated. The aim of this thesis was to study the involvement of five PLLs with highly upregulated gene expression in the grafting data sets during vascular development, primarily xylem development, and vascular regeneration. Arabidopsis loss-of-function mutants of the five PLLs were analysed with various assays including root tip regeneration, cell wall enzyme assays, hypocotyl micrografting and VISUAL, a method for observing xylem development. Mutants of the genes PLL22 and PLL26 exhibited reduced xylem development in VISUAL whereas the regeneration and grafting experiments showed insignificant effects on vasculature in all pll mutants. The obtained results suggest PLL22 and PLL26 affects in vitro xylem development in cotyledons and that there is possibly redundancy between PLL genes during vascular regeneration.