Doctor of Philosophy / Department of Biology / Michael A. Herman / The polarities of several cells that divide asymmetrically during C. elegans development are controlled by Wnt signaling. LIN-44/Wnt and LIN-17/Fz control the polarities of cells in the tail of developing C. elegans larvae, including the male-specific blast cell, B, which divides asymmetrically to generate a larger anterior daughter and a smaller posterior daughter. We determined that the canonical Wnt pathway components are not involved in the control of B cell polarity. However, POP-1/Tcf is involved and asymmetrically distributed to B daughter nuclei. Aspects of the B cell division are reminiscent of the divisions controlled by the planar cell polarity (PCP) pathway that has been described in both Drosophila and vertebrate systems. We identified C. elegans homologs of Wnt/PCP components and have determined that many of them appear to be involved in the regulation of B cell polarity and POP-1 asymmetric distribution to B daughter nuclei. Thus a non-canonical Wnt pathway, which is different from other Wnt pathways in C. elegans, but similar to the PCP pathways, appears to regulate B cell polarity. Molecular mechanisms of this PCP pathway were also investigated. We determined that LIN-17/Fz is asymmetrically distributed to the B cell cortex prior to, during, and after, division. Furthermore, the asymmetric localization of LIN-17::GFP is controlled by LIN-44/Wnt and MIG-5/Dsh. The cysteine rich domain (CRD), seven trans-membrane domain and KTXXXW motif of LIN-17 are required for LIN-17 to rescue lin-17, while only seven trans-membrane domains and KTXXXW motif are required for LIN-17 asymmetric localization. MIG-5::GFP asymmetrically localized to the B cell prior to and after division in a LIN-17/Fz dependent manner. We examined the functions of these MIG-5 domains. The DEP domain is required for MIG-5 membrane association, while the PDZ domain is responsible for different levels of MIG-5 in the B daughters. The DEP and PDZ domain are required to rescue B cell polarity defect of mig-5 males, while the DIX domain is not that important. In summary, a novel PCP-like pathway, in which LIN-17 and MIG-5 are asymmetrically localized, is conserved in C. elegans and involved in the regulation of B cell polarity.

Doctor of Philosophy / Agronomy / Allan K. Fritz / Bikram S. Gill / Gary M. Paulsen / Post-anthesis high temperature stress in wheat (Triticum aestivum L.) is a major cause of yield reduction. This process results in the loss of viable leaf area and a decrease in green leaf duration ultimately causing a yield loss. The objectives of this study were to (i) phenotype a recombinant inbred line population for heat tolerance traits, (ii) understand the genetic basis of heat tolerance by mapping quantitative trait loci (QTL) linked to yield-related traits under high temperature, (iii) model stay-green under high temperature stress and map the QTL linked to stay-green parameters, and (iv) validate the markers linked to QTL under field conditions. A filial6:7 (F6:7) recombinant inbred line (RIL) population was developed by crossing Ventnor, a heat-tolerant white winter wheat with Karl 92, a relatively heat susceptible hard red winter wheat. From 10 DAA to maturity, the treatments of optimum temperature or high temperature stress (30/25°C) were imposed on the RILs. The traits measured included grain filling duration (GFD), kernels per spike, thousand kernel weight (TKW), and grain filling rate (GFR). The stay-green traits calculated were: i) time between 75% and 25% green, ii) maximum rate of senescence, iii) time to maximum rate of senescence, and v) percent green at maximum senescence. Genetic characterization was performed using microsatellite (SSR), amplified fragment length polymorphism (AFLP) and a sequence tag site (STS) markers. GFD was positively correlated with TKW and negatively with GFR and maximum rate of senescence. Principle component analysis (PCA) showed kernels per spike, maximum rate of senescence, and TKW accounted for 98% of total variability among the genotypes for heat tolerance. The most significant QTL for yield traits co-localized with marker Xgwm296 for TKW, Xgwm356 for kernels per spike, and Xksum61 for GFR. The QTL for stay-green traits co-localized with markers P41/M62-107 on Chromosome 2A, Xbarc136 on Chromosome 2D, P58/MC84-146 on Chromosome 3B, P58/M77-343 on Chromosome 6A, and. P58/MC84-406 on Chromosome 6B. These results indicate that increased green leaf area duration has a positive effect on the grain yield under high temperature. Once the kernels per spike are established, GFD and TKW can be used as selection criteria for post-anthesis heat-tolerance.