Identification of QTL associated with root architecture under well-watered, and water-stressed conditions in Zea mays [abstract]

Abstract only availableFaculty Mentor: Dr. Georgia Davis, Microbiology and ChemistryDrought alone contributes 17% to the average annual yield loss in maize (Zea mays). It is the single most significant environmental obstacle to improving grain yield. Many physiological traits have been linked to drought resistance including osmotic adjustment, anthesis-silking interval, leaf surface area and root architecture. QTL associated with root architecture play an integral role in drought resistance by facilitating the uptake of water from sources deep below the soil line. Our goal was to identify the QTL involved in root architecture in Zea may under well-watered, and water-stress conditions. Two QTL experiments were performed one well-watered and one water-stressed. In the well-watered experiment, a subset of 94 mapping lines from the intermated B73 x Mo17 (IBM) population was planted in five reps in a randomized complete block design. The seed was sown in a peat based growth medium and the plants were grown in a greenhouse under well-watered conditions for two weeks. After the two-week period, shoot mass, root branching, primary root length, seminal root number and root mass were measure for each plant. The water-stressed experiment was conducted in the same manner. To prevent immediate desiccation of the plants a polyacrylamide water retainer was added to the growth media. After the initial two week, well-watered period the plants were allowed to grow without water for ten days. At the end of the 10 days the same traits were measured along with the relative water content of the 4th leaf. Genotypic data for 251 markers, evenly distributed throughout the maize genome, were used to construct a genetic map with Mapmaker Exp version 3.0 for Unix. QTL analysis was performed by using QTL Cartographer version 1.16. 32 total QTL were identified, 20 for the well-watered traits, and 12 for the water-stressed traits. The 20 QTL identified in the well-watered experiment accounted for 74%, 38%, 77% and 81% of the phenotypic variance in primary root length, root branching, seminal root number and shoot mass respectively. The 12 QTL identified in the water-stressed experiment accounted for 25%, 13.5%, 41.2%, 17.2%, of the phenotypic variance in primary root length, root branching, seminal root number and root mass. QTL identified were compared to previous QTL experiments. Many of the well-watered QTL correspond to QTL regions previously identified in other root architecture studies. Novel QTL for root growth under water-stressed were identified in bins 3.05

Pathway approaches to dissecting the inheritance of maize shoot-borne roots

Title from PDF of title page (University of Missouri--Columbia, viewed on April 21, 2014).Shoot-borne roots are essential plant components. Two pathway-based approaches were pursued to increase our understanding of genetic mechanisms controlling shoot-borne root patterning. The first pathway approach characterized the contribution of gibberellic acid-related genes in shoot-borne root patterning. Quantitative trait loci mapping in the Intermated B73xMo17 linkage mapping population identified chromosome regions controlling shoot-borne root patterning which also contained gibberellic acid biosynthetic and response genes. Phenotyping of mutants with altered gibberellic acid production and response validated these genes as potentially underlying the identified quantitative trait loci. Association analysis was conducted in a set of 260 diverse maize inbred lines. The association analysis identified significant polymorphisms in the catalytic domain of the gibberellic acid biosynthetic gene dwarf3 and in the promoter region of the gibberellic acid response regulator Dwarf8. These results confirmed the previous hypothesis that gibberellic acid production is involved in shoot-borne root patterning and expanded it to include DELLA-mediated gibberellic acid response. In the second pathway-based approach a multivariate phenotypic analysis was conducted on 25 diverse maize inbred lines that were phenotyped for 23 developmental traits along with three shoot-borne root traits to define novel hypotheses about pathways involved in shoot-borne root patterning,. Evidence for a light-signaling component in root development was found. Further support for the involvement of light-signaling was provided by mutant phenotyping and field experiments which confirmed the predictions of the multivariate analysis. The two pathways were integrated into one model where light-mediated redistribution of gibberellic acid dictates shoot-borne root patterning

The ramosa1 gene plays a role in shoot-borne root patterning in Zea mays L.

Abstract only availableMaize brace roots are the aerial portion of the shoot-borne root system that facilitates physical anchorage and water and nutrient acquisition. Shoot-borne roots develop from axillary meristems. Axillary meristems can also give rise to leaves and tillers and are important in inflorescence development. Evidence is accumulating that similar genes are involved in at least the early stages of axillary meristems development regardless of meristems fate. According to a previous quantitative loci mapping study on brace roots architecture the ramosa1 gene is a positional candidate for controlling brace root variation. ramosa1 (ra1) affects the development of maize tassels by suppressing tassel branching and promoting spikelet pair formation. Mutations in the ra1 results in a greater number of tassel branches that grow increasingly shorter near the apex of the tassel. A correlation analysis between tassel traits and root traits was performed using 25 diverse maize lines. The results show a significant and positive correlation between various brace roots traits and tassel branch length, a trait controlled by ra1. Further more, a comparison of ramosa1 mutant to wild-type plants revealed statistically significant differences in root phenotypes with the ra1 mutants producing fewer brace roots at a node and fewer nodes with brace roots. This suggest that ra1 is part of both the inflorescence and shoot-borne root development programs Mutations in ra1 appear to have opposite effects on maize brace roots relative to tassels indicating that the role of ra1 may differ depending developmental phase. This research was supported by the NSF UMEB Program, Life Science Mission Enhancement, and USDA ARS.NSF Undergraduate Mentoring in Environmental Biolog

Influence of miRNA on brace root patterning in Zea mays L.

Abstract only availableBrace roots reduce lodging by providing support and represent the majority of the root system in adult plants. Previous quantitative trait locus mapping results showed that Teopod1 (Tp1), Teopod2 (Tp2), and Corngrass1 (Cg1), all mapped in chromosome regions which influence brace root patterning. Tp1 and Tp2 are semi-dominant mutants and Cg1 is a dominant mutant that result in delayed-phase-change and overlap between the juvenile and reproductive phases. Gibberellic acid (GA) promotes phase change and exogenous GA alters Tp1 and Tp2 phenotype . Prior analysis of GA mutants in our laboratory and others indicates that GA affects brace root patterning. We performed a means comparison between Tp1 and Tp2 and their wild-type siblings and identified significant differences in brace roots traits, specifically, mutants exhibited more nodes with brace roots and more brace roots at a node than their wild-type counterparts. Cg1 encode a member of the miR156 family which is known to target squamosa promoter-binding (SPB)-like proteins. Tp1 and Tp2 have also been suggested to encode members of the miR156 family. To further validate the role of miRNA156 in brace root patterning, we performed association analysis with available sequence from the parents of the nested association mapping (NAM) population and brace root trait data. Preliminary analysis supports the involvement of miRNA156 family members in brace root patterning. Additional sequencing of miRNA156 in a larger group of maize lines is underway to provide a more robust dataset for association analysis.Missouri Academy at Northwest Missouri State Universit

Quantitative trait loci for seminal root angle and number in the maize IBM population

Abstract only availableIn maize, seminal roots develop and the primary root system deteriorates as the plant matures. The seminal roots comprise the majority of the root system of the adult plant and give the plant stability against lodging. Because seminal roots are the primary means of water uptake in the adult plant, their development under drought conditions is vital. Previous research has suggested that seminal root angle and abscisic acid (ABA) level are correlated in maize. Additional research has shown that ABA levels are related to drought tolerance. This study focuses on identifying quantitative trait loci (QTL) that affect seminal root angle and the number of seminal roots entering the soil from each node. The QTL generated for seminal root angle and number per node can then be used to evaluate the relationship with drought tolerance. A set of 94 mapping lines from the intermated B73 x Mo17 (IBM) mapping population was used to measure the angle between the seminal root and the stalk. The number of seminal roots entering the soil from the first two nodes was measured as well. Molecular markers evenly distributed throughout the genome were used to run the QTL analysis using QTL Cartographer Version 1.16. The following QTL analyses were run: seminal root angle, number of roots entering soil from the first node above ground, and number of roots entering soil from the second node. Three QTL were found for seminal root angle, two QTL for the number of roots at the first node above ground, and three QTL for the number of roots at the second node above ground. These QTL positions were then compared to previously known QTL for drought tolerance and root traits.Plant Genomics Internship @ M

Modeling the relationship between light perception traits and brace root development in Zea mays L. [abstract]

Abstract only availableMaize (Zea mays L.) brace roots are responsible for physical stability in the soil and for water and nutrient acquisition in maize. The objective of this project is to investigate how traits related to light perception affect brace root development. Previous work has shown that light perception affects total root development and that reduced lighting conditions cause a decline in all root growth, even more drastically than in the rest of the plant (Y. Hébert, E. Guingo, and O. Loudet, 2001). Trait data for 98 diverse lines were collected primarily from 2004 to 2005 for traits related to light perception and maturity. Correlation analysis and multiple regression analysis were performed to produce models that identify traits significantly affecting brace root development and their interactions. Our model shows that in 2005, light perception traits were not as significant as in 2004 indicating that the effect of light perception on brace root number may be environmentally dependent. This could be because the much hotter temperatures in 2005 caused the light perception mechanism to be saturated masking the interaction, whereas in 2004, the temperate environment caused the expression of the light perception and brace root interaction. The experimental model will then be validated using data collected on the identified traits from 25 diverse lines grown in the field

Traits associated with brace root characters implicate light and hormonal signaling pathways [abstract]

Abstract only availableMaize brace roots provide the plant with access to water and nutrients in the soil, increase stability, and improve lodging resistance. The goal of this study is to connect brace root traits to traits linked to developmental and hormonal pathways, and light perception by multiple regression and correlation analysis. Two replications of twenty-seven diverse lines of maize were planted and measured for light perception traits, maturity and phase transition traits, in the summer of 2007. Forward selection and backwards elimination multiple regression and correlation analysis were performed in SAS. A significance threshold of 0.05 for entry or elimination was used in the multiple regression analysis. Model R-squared values had a range of 0.47 to 0.64. The variables significant for the number of nodes with brace roots and the number of brace roots at node one were related to the growth hormone gibberellic acid (GA) such as average internode length and juvenile and transition leaf number. Soil node diameter and ear height were also linked to root traits and are under the genetic control of the light response regulators phytochromes B1 and B2. A proposed model showing how GA and light perception affect plant development is reported. This research was funded by the Undergraduate Mentoring in Environmental Biology and The Life Science Mission Enhancement programs.NSF Undergraduate Mentoring in Environmental Biology; The Life Science Mission Enhancement Progra

QTL analysis for genes for brace root angle in zea mays l. [abstract]

Abstract only availableBrace roots play a major role in determining amount of lodging, and are responsible for a significant portion of water and nutrient uptake. Using the randomly intermated B73 x Mo17 (IBM) RIL mapping population, we are identified chromosome regions which control brace root development. Previous work analyzed data from 94 mapping lines and identified numerous QTL. The number of potential candidates within these QTL intervals is too large to realistically test. For this reason, we are utilizing a larger number of mapping lines from this population in combination with additional markers, especially within known QTL regions, to refine the QTL intervals and reduce the number of candidate genes. The IBM mapping population was evaluated in the field in two replications in the summer of 2006. Pictures were taken and brace root angles were measured digitally using Image J. Analysis of variance was performed in SAS (SAS Institute, Raleigh, NC) with replicates and lines as main effects. Both replicates and lines had significant variation. Transgressive segregants were identified. A genetic map was generated using Mapmaker Experiment 1.16 with markers evenly spaced throughout the genome. Composite interval mapping was conducted using QTL cartographer 3.0 for Unix. Candidate genes are currently being identified through comparison of our mapping results with the Maize Bins, the IBM neighbors map (a computationally-derived composite map containing more than 14,000 genes and mutants mapped by the entire maize genetics community), and the 2005 Genetic Map.MU Monsanto Undergraduate Research Fellowshi