MOLECULAR AND CELLULAR BASIS OF FUSARIUM WILT IN ARABIDOPSIS
Open Access
- Author:
- Kim, Hye-Seon
- Graduate Program:
- Plant Pathology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 09, 2008
- Committee Members:
- Seogchan Kang, Committee Chair/Co-Chair
Charles Peter Romaine, Committee Member
Timothy W Mcnellis, Committee Member
Maria Del Mar Jimenez Gasco, Committee Member
Majid R Foolad, Committee Member - Keywords:
- Fusarium
Arabidopsis
Pathogenicity
Calcium biosensor - Abstract:
- Although the persistence of soil-borne fungal pathogens continually poses a serious threat to the sustainability of the production of many crop plants, only a very limited number of control strategies exist to manage soil-borne fungal diseases in part due to a limited understanding of the biology and ecology of soil-borne fungi. Current paradigms on the molecular and cellular basis of plant-pathogen interactions have been mostly derived from foliar diseases. The number of model systems for studying soil-borne diseases is limited. The main goal of this thesis work is to study the molecular and cellular mechanisms underpinning soil-borne fungal diseases through the use of a new model system, based on Arabidopsis thaliana as the principal host and Fusarium oxysporum as the primary pathogen. F. oxysporum causes vascular wilt and root rot diseases in a wide variety of plant species, including A. thaliana. Using a combination of molecular and cytological tools, I investigated the role of the cAMP-dependent protein kinase A gene in F. oxysporum (named as FoCPKA) in pathogenesis of Arabidopsis thaliana. Disruption of FoCPKA causes several mutant phenotypes, including complete loss of pathogenicity with no penetration/colonization of the vascular system, reduced vegetative growth and conidiation, reduced root attachment by spores, and an altered hyphal growth pattern. Preliminary functional characterization of two additional F. oxysporum genes, including NUC2 (Negative regulator of phosphorous acquisition) and ZRT2 (Iron/zinc transporter), has also been conducted. To monitor real-time cellular and physiological changes during host-pathogen interactions, I report here the first successful expression of a FRET (Fluorescence Resonance Energy Transfer)-based calcium sensor in two plant pathogenic fungi, F. oxysporum and Magnaporthe oryzae. Time-lapse imaging of live fungal cells expressing this sensor revealed the presence of transient tip high Ca2+ gradient that occurs in a pulsate manner. Examination of dynamic changes in cytosolic Ca ([Ca2+]c) suggested that Ca2+ might play important role in regulation of hyphal branching, septum formation, and cell-cell contact during fungal growth. The same sensor was also introduced into three A. thaliana ecotypes that differentially interact with F. oxysporum as a first step to investigate how host responses to fungal infection are controlled via calcium. Increased knowledge about dynamic Ca2+ changes using this Ca2+ sensor offers novel opportunities for understanding mechanisms underlying signal transduction changes in response to external stimuli during plant-pathogen interaction. A different calcium sensor and a pH sensor based on modified single green fluorescent proteins have also been developed, and their utilities for probing physiological changes in fungal and plant cells and at their interfaces are currently being evaluated. In combination with the genetic and molecular cytology tools described here, genome sequences of A. thaliana and F. oxysporum and other experimental tools should help us dissect the genetic, cellular, and biochemical basis of Fusarium wilt.