| Roots growing on tilted hard surfaces have been studied in attempt to better understand plant tropic responses to gravity and touch in concert with intrinsic cellular processes like circumnutation and cytoskeleton dynamics. The purpose of this dissertation is to summarize the knowledge we have gained from these studies, and then explore what more can be learned through the natural variation that exists for the root growth behaviors of waving and skewing.;Many of the genes found to affect root growth behaviors on tilted hard agar surfaces produce proteins involved in the organization of the plant cytoskeleton. In Chapter 1, we explore how mutations in tubulin, tubulin-associated genes, various cell wall components, and signaling pathway proteins affect root skewing and waving. From the mutant studies, it is clear that proper microtubule dynamics and intact signaling cascades are critical to the execution of these complex growth behaviors.;In Chapter 2, we look at natural variation in Arabidopsis root growth behaviors. Using a recombinant inbred line (RIL) population created from the natural accessions Cvi and Ler, several quantitative trait loci (QTL) were found for these traits. Through use of near isogenic lines (NILs), we have confirmed a skewing QTL on chromosome 2 in a region where no known contributors to this behavior are located. An expression study indicates genes involved in cell wall composition may be contributing to the skewing phenotype.;Chapter 3 also consists of a QTL study for root growth behavior in the Cvi/Ler RIL population, but here the assay was changed by applying exogenous cadaverine to the seedlings. Cadaverine is a polyamine, which are compounds involved in numerous basic cellular processes as well as stress responses. We have focused on a QTL predicted to contribute to the affect of cadaverine on root length. This QTL has also been confirmed through use of NILs. Expression analysis led us to OCT1, an organic cation transporter that is at higher transcript levels in Cvi, as a candidate gene. |
