Anther culture of Sorghum bicolor (L.) Moench

Call number: LD2668 .T4 AGRN 1988 W46Master of ScienceAgronom

The Tumor Suppressive Role of eIF3f and Its Function in Translation Inhibition and rRNA Degradation

Deregulated translation plays an important role in human cancer. We previously reported decreased eukaryotic initiation factor 3 subunit f (eIF3f) expression in pancreatic cancer. Whether decreased eIF3f expression can transform normal epithelial cells is not known. In our current study, we found evidence that stable knockdown of eIF3f in normal human pancreatic ductal epithelial cells increased cell size, nuclear pleomorphism, cytokinesis defects, cell proliferation, clonogenicity, apoptotic resistance, migration, and formation of 3-dimensional irregular masses. Our findings support the tumor suppressive role of eIF3f in pancreatic cancer. Mechanistically, we found that eIF3f inhibited both cap-dependent and cap-independent translation. An increase in the ribosomal RNA (rRNA) level was suggested to promote the generation of cancer. The regulatory mechanism of rRNA degradation in mammals is not well understood. We demonstrated here that eIF3f promotes rRNA degradation through direct interaction with heterogeneous nuclear ribonucleoprotein (hnRNP) K. We showed that hnRNP K is required for maintaining rRNA stability: under stress conditions, eIF3f dissociates hnRNP K from rRNA, thereby preventing it from protecting rRNA from degradation. We also demonstrated that rRNA degradation occurred in non-P body, non-stress granule cytoplasmic foci that contain eIF3f. Our findings established a new mechanism of rRNA decay regulation mediated by hnRNP K/eIF3f and suggest that the tumor suppressive function of eIF3f may link to impaired rRNA degradation and translation

Inducible expression of Pisum sativum xyloglucan fucosyltransferase in the pea root cap meristem, and effects of antisense mRNA expression on root cap cell wall structural integrity

Mitosis and cell wall synthesis in the legume root cap meristem can be induced and synchronized by the nondestructive removal of border cells from the cap periphery. Newly synthesized cells can be examined microscopically as they differentiate progressively during cap development, and ultimately detach as a new population of border cells. This system was used to demonstrate that Pisum sativum L. fucosyl transferase (PsFut1) mRNA expression is strongly expressed in root meristematic tissues, and is induced >2-fold during a 5-h period when mitosis in the root cap meristem is increased. Expression of PsFut1 antisense mRNA in pea hairy roots under the control of the CaMV35S promoter, which exhibits meristem localized expression in pea root caps, resulted in a 50–60% reduction in meristem localized endogenous PsFut1 mRNA expression measured using whole mount in situ hybridization. Changes in gross levels of cell wall fucosylated xyloglucan were not detected, but altered surface localization patterns were detected using whole mount immunolocalization with CCRC-M1, an antibody that recognizes fucosylated xyloglucan. Emerging hairy roots expressing antisense PsFut1 mRNA appeared normal macroscopically but scanning electron microscopy of tissues with altered CCRC-M1 localization patterns revealed wrinkled, collapsed cell surfaces. As individual border cells separated from the cap periphery, cell death occurred in correlation with extrusion of cellular contents through breaks in the wall

Root Border Cell Development and Functions of Extracellular Proteins and DNA in Fungal Resistance at the Root Tip

Soilborne plant pathogens are responsible for many of the major crop diseases worldwide. However, plant root tips are generally resistant to pathogen infections. The goal of this dissertation research is to understand the mechanism of this natural resistance by testing the hypothesis that root caps and root border cells control the rhizosphere community through the biological products which they deliver to the soil. Specific objectives of this dissertation project are 1) identifying, isolating, and characterizing the genes important for border cell development and for root exudates delivery, and 2) analyzing the function of extracellular macromolecules in root exudates in root tip-fungal pathogen interaction. The expression of a primary cell wall synthesis gene, PsFut1, encoding Pisum sativum fucosyltransferase, was characterized during border cell production, and the impact of silencing this gene on border cell development was examined. Another gene, BRDgal1, encoding β-galactosidase, was identified and characterized in Pisum sativum during this study. It was shown that this β-galactosidase is specifically produced in and secreted from root border cells. The microarray transcriptional profiling in M. truncatula and mRNA differential display analysis in pea plants were carried out following the induction of border cell production to gain a broader understanding of the genes which potentially influence border cell development. In order to study the commonality of border cell production across different plant species, the expression of rcpme1, the marker gene for border cell production, was compared between the garden pea and a gymnosperm species, the Norway spruce (Picea abies). To accomplish the second objective, the focus of this study was shifted from border cell development to mucilaginous root exudates excreted by border cells and root cap cells. This resulted in a breakthrough in the understanding of the mechanisms of root tip resistance. The presence of extracellular DNA in the root mucilage was discovered and its requirement for root tip resistance to fungal infection was demonstrated. Extracellular proteins in the root mucilage were identified and they were shown to be also required for the root tip resistance to fungal infection. This work provided new insights into understanding plant defense mechanisms