Document Type

Dissertation - Open Access

Award Date

2016

Degree Name

Doctor of Philosophy (PhD)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Karl D. Glover

Keywords

autiimmunity, hybrid necrosis in wheat, Ne1 and Ne2 genes, reactive oxygen species, RNA-seq, xanthine dehydrogenase

Abstract

Expression of hybrid necrosis in plants can lead to a significant reduction in productivity, or even lethality. Epistatic interactions between divergent loci that have evolved through evolution are proposed as being responsible for the genetic incompatability that is expressed as hybrid necrosis. Hybrid necrosis can also represent an obstacle to the transfer of desirable traits from wild, related species to domesticated bread wheat. In wheat, expression of dominant complementary genes Ne1 and Ne2, located to chromosomes 5B and 2B in a hybrid results the production of necrotic leaf tissue, stunted plant growth, and reduced grain yield, which are similar plant responses to many biotic and abiotic stresses. This study was undertaken to compare the molecular genetic and physiological hybrid necrotic responses in wheat with those typically observed for biotic and abiotic stresses. Objectives were to; (1) measure levels of reactive oxygen species (ROS) and , xanthine dehydrogenase (XDH) during wheat hybrid necrosis, (2) assess the impact of temperature on the expression of hybrid necrosis, (3), assess the allelic interactions responsible for necrosis, and (4) characterize the genes upregulated during the expression of hybrid necrosis in wheat. The production of H2O2 in hybrid necrotic plants was not significantly different than in non-necrotic parents, suggesting that unlike some stress responses, elevated H2O2 levels are not responsible for causing programmed cell death and tissue necrosis in wheat. Reduced plant growth and yield in the allopurinol treated plants, and those plants expressing suppression of XDH affirms the role of XDH in purine catabolism and most likely nitrogen reassimilation in plants. Similar to the temperature sensitive expression of some disease resistance genes in wheat, expression of necrosis symptoms was reduced when hybrids were grown at 30OC. The SSR markers; Xbarc7, Xbarc13 and Xwmc344 are linked to the Ne2 gene at distances of 3 cM, 4 cM, and 6 cM, respectively, and Xgwm639 is linked at 11 cM with Ne1. There was an observed dosage effect associated with the Ne alleles, and both ‘Alsen’ and synthetic hexaploid wheat line ‘TA 4152 -37’ expressed moderate necrosis due to the Nem alleles. Gene expression analyses revealed that defense signaling genes were highly up-regulated during the expression of hybrid necrosis along with the activation of several antioxidant enzymes. Detection of high levels of polyamine oxidase activity during hybrid necrosis suggests that this enzyme could be the main source of ROS responsible for tissue cell death. Genes typically encoding for plant recognition receptors (PRRs), pathogenesis–related proteins, antioxidant enzymes, calcium regulation, protein kinases and ethylene biosynthesis were all up-regulated during expression of wheat hybrid necrosis. Results support the concept that hybrid necrotic symptoms in wheat are the byproduct of an autoimmune type of response similar to many responses invoked by wheat plants when exposed to a biotic, or abiotic stress.

Library of Congress Subject Headings

Wheat -- Diseases and pests -- Molecular genetics.

Necrosis.

Wheat -- Effect of stress on.

Autoimmunity.

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

227

Publisher

South Dakota State University

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Rights Statement

In Copyright