Characterisation of new genes involved in Arabidopsis vascular development

Abstract

The vascular system of plants is composed of two main tissues: the xylem and phloem, which arise from meristematic cells positioned between them. Xylem is the woody tissue responsible for water transport, while the phloem transports photosynthates. PHLOEM INTERCALATED WITH XYLEM (PXY) is a receptor-like kinase, which in cooperation with its peptide ligand TRACHEARY DIFFERENTIATION INHIBITORY FACTOR (TDIF), controls the formation and maintenance of the vascular tissue. Despite the crucial importance of PXY-TDIF in controlling vascular development, the principles coordinating these elements remain unknown. TDIF is derived from CLE41, but the mechanism whereby CLE41 is cleaved into TDIF, TDIF secretion by phloem cells, and events in the cytoplasm following TDIF binding to PXY is unknown. Where some components of TDIF-PXY signalling have been described, interacting factors are not known. Consequently, knowledge of PXY signalling remains somewhat limited. To identify new components of TDIF-PXY signalling, a mutagenesis screen was performed in lines over-expressing TDIF. In this thesis, wa3 and wa10 were identified as suppressors of the TDIF over-expression phenotype, and were thus hypothesised to encode components of PXY signalling. The wa3 lesion was not identified, but wa10, characterised by a complete suppression for 35S::CLE41 was found to encode a WD40/transducing domain-containing protein, which we renamed PUCK. Further alleles were used to verify that mutations in PUCK could suppress CLE41 overexpression phenotypes. Genetic interactions with pxy, er and bp were also analysed.