Date of Award
Doctor of Philosophy
Genetics, Development and Cell Biology
Diane C. Bassham
Cellular trafficking of cargo vesicles at the trans-Golgi network (TGN) is required for multiple processes such as cell expansion, stress responses and hormonal transport in plants. Activity of membrane proteins known as SNAREs drives membrane fusion events. Associated proteins such as tethering factors and Sec1/Munc18 proteins aid the fidelity and efficiency of these fusion events by interacting with SNAREs. The TGN-localized SYP41/SYP61/VTI12 SNARE complex is required for vacuolar and secretory cargo trafficking.
TNO1, a putative tethering factor, associates with SYP41 and is required for TGN membrane fusion dynamics and proper SYP61 localization. My dissertation research discovered a new role of TNO1 in auxin transport-related physiology. Mutants lacking TNO1 (tno1) display decreased gravitropic bending of plant organs, delayed lateral root emergence and increased sensitivity to natural auxin and a cell influx-specific synthetic auxin. Reduced auxin asymmetry at the tips of elongating lateral roots and gravistimulated primary root tips in the mutants confirms TNO1’s role in cellular auxin transport during these processes. Loss of TNO1 does not affect bulk endocytosis and arrival of membrane cargo at the TGN, suggesting a specific effect of TNO1 in auxin transport mechanisms by possibly affecting subcellular trafficking of auxin transporters.
The root gravitropic defects led me to hypothesize that root growth movements would be defective in the tno1 mutants. I discovered that tno1 mutant roots display exaggerated rightward deviation from the growth trajectory (skewing), correlated with an enhanced left-handed root epidermal cell file rotation, when grown on slanted impenetrable growth media. tno1 mutants also behave differently from wildtype in studies investigating the effect of microtubule-disrupting drugs on root skewing and cell expansion show. This suggests that TNO1 might have a role in microtubule-associated mechanisms driving skewing and cell expansion, though a direct effect on MT array orientation was not observed. Altogether, this suggests TNO1’s role in both auxin transport and possibly MT-associated processes.
I also investigated the effect of a point mutation in VPS45, a SYP41-associated Sec1/Munc18 protein. The mutant (Atvps45-3) displays dwarf phenotypes with highly reduced plant organ sizes and cell expansion. Mutant root hairs are short and thick compared to wildtype root hairs, suggesting defects in polarized cell expansion processes. The endocytic and secretory routes in Atvps45-3 plants seem unaffected suggesting a specific effect of the mutation on cell expansion.
Taken together, these results add to the knowledge of SNARE-associated proteins at the TGN and how post-Golgi traffic mediates lateral root emergence, gravitropism, root movement and root hair expansion.
Roy, Rahul, "TNO1 & VPS45: SNARE-associated proteins required for plant growth" (2016). Graduate Theses and Dissertations. 15067.