Abstract
In this dissertation, two independent research studies will be presented. The following are the abstracts for each study: Chromatin structure plays an important role in gene expression. Chromatin remodeling complexes (CRC) are responsible for modifying the structure of chromatin at specific sites in the genome during different developmental stages. SWR1 is a CRC that functions to replace canonical histone H2A with variant H2A.Z which is associated with altered gene expression. Several subunits have been characterized in model plant Arabidopsis thaliana including PIE1, ARP6, SWC6, SWC4, SWC2, and MBD9; however, a known subunit in yeast (SWC5) and homo sapiens (craniofacial development protein), has never been characterized in A. thaliana and no SWR1 subunits have been identified in model crop plant Solanum lycopersicum. In this study we identify and characterize A. thaliana and tomato SWC5 as a subunit of the CRC SWR1. Mutant Atswc5 share the same abnormal phenotypes with other SWR1 mutant lines such as early flowering, loss of apical dominance, and smaller, narrower leaves. A new phenotype of SWR1 mutant lines was discovered of increased salt sensitivity at germination being observed in Atarp6-1 and both Atswc5 mutants. AtSWC5 localizes primarily in the nucleus and directly interacts with AtARP6 . For tomato, SlSWC5 also interacts directly with SlARP6, SlPIE, and SlH2A.Z variants. Interestingly, Slswc5 knockdown lines showed, reduced plant height throughout all growth stages, loss of lobing on leaves, were more resistant to Psuedomas syringae pv. tomato infection produces smaller fruits which had lower soluble sugar content and drastically reduced seed set. Taken together SWC5 is an essential subunit of the CRC SWR1 and functions to regulate genes involved with plant morphology, fruit development, abiotic and biotic stress response.
The plant-parasitic nematode (PPN) Globodera pallida is an obligate biotroph that only reproduces on select species in the Solanum family. The establishment of the feeding site, the syncytium, involves secretion of effectors into the plant cell to combat the plant defense response and facilitate transformation of root cells into the syncytium. Despite the important predicted roles of effectors in the plant-pathogen interactions, the functionality of G. pallida effectors is largely unknown. In this study, we identified and characterized a G. pallida effector protein disulfide isomerase (GpPDI1). GpPDI1 contains two thioredoxin domains that function together to reduce disulfide bonds, as manifested by the nullification of enzymatic activity when either domain is absent. The transcript of GpPDI1 is localized in the dorsal gland of the nematode during the J2 stage. In addition, GpPDI1 can trigger defense-related cell death in Nicotiana benthamiana and tomato (Solanum lycopersicum) leaf tissue and localizes in the plant host cell’s cytoplasm and nucleus when transiently expressed in plant cells. Significantly, the ability of elicitation of cell death is not dependent on the enzymatic activity of GpPDI1 or correlated with the subcellular distribution of GpPDI1, suggesting that a non-disulfide reducing function or structural feature of GpPDI1 is responsible for the recognition by the host immune system to elicit cell death.