Date of Award

2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Biology

First Advisor

Kimberly L. Gallagher

Abstract

How organisms sense external cues and integrate them into developmental changes remains a large biological question. Plants, which are sessile organisms, are particularly vulnerable to challenges in their environment. An early response to abiotic and biotic stress in plants is the modification of intercellular signaling through plasmodesmata, cytoplasmic channels that connect adjacent cells. However, the different ways in which plasmodesmata-mediated signaling can be affected, the molecular players involved in this response, the genetic basis of this regulation, and the biological benefits of this response are still poorly understood.

Here, we take a survey of seven different agriculturally relevant stresses of nutrient starvation and heavy metal contamination, and their effects on plasmodesmata transport in the A. thaliana root. We examine the role of the polysaccharide callose, a known plasmodesmata regulator, in these modifications. Focusing on the conditions of excess iron and copper, we take a genetic approach to identify the genes involved in callose metabolism under these conditions. Finally, we examine how modifications in plasmodesmata transport under stress affect plant growth, health, and tolerance to heavy metal stress.

We find that plasmodesmata closure in response to stress is not a universal response, as was previously believed. While most conditions do induce plasmodesmata closure, some heavy metals increase plasmodesmata permeability instead. In many of the conditions tested, the changes in plasmodesmata modification correlate with changes in callose deposition as expected. In further examining excess copper and iron stresses, we identify genes in the callose synthase and β-1,3-glucanase families that synthesize and breakdown callose, responsible for callose metabolism under these conditions. We observe that these regulated changes in plasmodesmata signaling in response to stress affect root growth, health, and mineral distribution. Most importantly, opening plasmodesmata under excess copper allows for better root growth, improved tolerance to copper, and reduced copper levels in the root meristem.

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