Genetics, Development and Cell Biology Ph.D. candidate: Yosia Mugume

Major: Genetics and Genomics

Major Professor: Diane Bassham

Title: "Effect of Autophagy on Lipid Content and the Impact of VPS45 on Plant Growth in Arabidopsis Thaliana"

Abstract: Autophagy is an evolutionarily conserved mechanism in eukaryotic cells by which cytoplasmic materials and damaged cell components are packaged in autophagosome vesicles and trafficked to the vacuole for degradation and recycling for reuse by the cell. Also, newly synthesized proteins, enzymes, and storage proteins are transported to the vacuole by the vesicle trafficking pathway. In this dissertation, I focused on the two vesicle trafficking pathways, autophagy and vesicle trafficking, which deliver cargo to the vacuole.

Autophagy has been shown to influence plant metabolome, however its impact on plant lipidome is not fully understood. I investigated the impact of autophagy on lipid amounts in Arabidopsis. I demonstrated the use of Mass spectrometry imaging (MSI) with matrix-assisted laser desorption ionization (MALDI-MSI) to image lipids in situ in Arabidopsis. My results showed homogeneous distribution of lipids throughout the exposed interior leaf surfaces examined. This homogeneous distribution was unaffected by any of the mutations that we studied, nor was it affected by the nitrogen treatment that was applied to these plants, both of which affect autophagy. I observed changes in relative amounts of different lipids in the mutants compared to WT both under nitrogen replete and nitrogen deplete conditions. Relative amounts of poly unsaturated and very long chain lipids were significantly reduced in autophagy blocked mutants compared to WT. My results provide additional evidence that autophagy affects plant lipid content, and that autophagy likely affects lipid properties such as chain length and unsaturation.

VPS45 belongs to the Sec1/Munc18 family of proteins in Arabidopsis. This family of proteins interacts with and regulates Qa-SNAREs during membrane fusion. AtVPS45 interacts with the SYP61/SYP41/VTI12 SNARE complex located on the trans-Golgi network (TGN) and functions in cargo trafficking to the vacuole. I investigated the effect of a point mutation in VPS45 in Arabidopsis. The point mutant (vps45-3) displays dwarf phenotype with highly reduced plant organ sizes. Mutant root hairs are short and thick compared to WT hairs and also the pollen tube is significantly shorter compared to WT, suggesting defects in tip growth. vps45-3 also had vacuole defects characterized by many small vacuoles compared to WT which had one big vacuole. We propose that the observed compromise in tip growth in vps45-3 root hairs is due to the defects in vacuoles, since the vacuole is important for generation of turgor pressure needed for tip growth.

Taken together, these results show that MALDI-MS can be used for imaging lipids in situ and that autophagy has an effect on relative membrane lipid amounts in Arabidopsis. This work also shows the role of VPS45 in controlling tip growth in Arabidopsis.

Meeting link: https://augie.zoom.us/j/92840840767?pwd=cWk2cC9neWxyV1FIcUY1VE5pY3hrdz09

Meeting ID: 928 4084 0767

Passcode: 849639

Flyer: Yosia Mugume Ph.D. defense seminar