Lily Murchison is a Junior studying Engineering in a 3/2 program at Scripps College in Claremont, California. This summer Lily is a part of Dr. Ram Dixit’s lab and is investigating the causes of twisted growth as a result of the spiral1-3 and kclr1 twisted mutants in Arabidopsis. More specifically Lily will be analyzing how these microtubule defects effect cell morphology, growth rate, and microtubule orientation in the root of the plant.
The Role of the Microtubule Cytoskeleton in Helical Growth in Plant Roots
Roots are critical organs for finding needed nutrients for plants and using directional growth to avoid foreign obstacles. Plant roots, which are anatomically symmetrical, grow via turgor pressure-driven cell expansion. Plant cells are encompassed by cortical microtubules that guide the deposition of cell wall materials which reinforces the cell wall along the transverse axis in elongating cells and direct cell growth in the vertical direction. Mutations in proteins that interact with microtubules can cause helical growth. The spr1-3 mutant is a point mutation that tracks the growing plus-end of microtubules and produce a right-handed growth pattern. A skewed orientation of the microtubule array has been implicated in causing twisted plant growth in mutants, however the role of skewed microtubules in promoting twisted root growth is not well understood. Furthermore, it is unclear if twisting also occurs at the cell level. Using Arabidopsis thaliana, a commonly used plant for cytoskeletal research, we compared the spr1-3 mutant to wild-type Col-0 to better understand the role microtubule orientation has within this twisted phenotype and what relationship the microtubules have with the morphology of the cells, ultimately aiming to understand how patterns at the cytoskeletal and cell level contribute to this twisted phenotype. To assess if microtubules are skewed prior to the onset of root twisting, microtubule orientation in Col-0 and spr1-3 roots expressing a GFP-TUB6 marker were measured using the FibrilTool ImageJ tool. We found that microtubules in spr1-3 roots adopt a left-handed skew before twisting occurs, suggesting that skewed microtubule array may be what drives the twisting phenotype to occur at the organ level. To assess twisting at the cell level, morphometry of wall lengths and angles were compared between wild-type Col-0 and spr1-3 roots using ImageJ. From this we found that at the cell level symmetry breaks in lateral wall lengths whilst maintaining its symmetry in cell angles. This study will help further inform us how microtubule-level mutations affect cell-level and organ-level directional growth and can be used for future modeling of root skewing.