Characterization of the effects of auxin on root vascular development in DRAMAQUEEN mutant Arabidopsis

Abstract

The vascular tissue is crucial for transporting water and nutrients between the different parts of the plant. It consists of two main tissues, xylem and phloem. Xylem consists of protoxylem and metaxylem, with protoxylem developing first in the newest parts of the plant. Vascular development is regulated by plant hormones, such as auxin, cytokinin and abscisic acid, which interact with each other. DRAMAQUEEN (DRQ) is an unknown gene in Arabidopsis and other plants that might be involved in root vascular development. A partially functional DRQ mutant, mDRQ, was previously found to affect the root elongation rate and protoxylem phenotype, as well as increase cytokinin sensitivity in Arabidopsis, suggesting its role as a possible cytokinin inhibitor. In this thesis, three knockout DRQ mutant lines are checked for auxin sensitivity as part of a bigger research project aiming to unravel the role of DRQ in vascular development. The root length and xylem phenotype are compared to the naturally occurring genotype Col0 (wild type), and a mutant of AHP6, another cytokinin inhibitor, which displays some similarity to the mDRQ phenotype. The xylem anatomy was analyzed in the old, intermediate and differentiate zones of the Arabidopsis thaliana root.

Statistically significant differences were found in the protoxylem anatomy of the old and intermediate parts of the root, suggesting that DRAMAQUEEN affects protoxylem differentiation and is mostly expressed closer to the root beginning. DRQ mutants also displayed shorter roots than Col0 in all auxin concentrations, suggesting a possible higher auxin sensitivity. However, the inhibitory effect of exogenous auxin on the root elongation was similar between Col0 and the DRQ mutants.