This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

In plants, flowering time is a tightly regulated process where several environmental and endogenous cues fine-tune the time of flowering. In Arabidopsis, four major genetic pathways regulate flowering time, namely photoperiod, vernalization, autonomous, and phytohormone gibberellic acid (GA) pathways. Arabidopsis is a facultative long day (LD) plant. LD promotes flowering whereas flowering is delayed in short day (SD) conditions. Here, we identified a basic-helix-loop-helix (bHLH) transcription factor called bHLH93 that is necessary to promote flowering only in SD. Also, photoperiod plays more critical roles in regulation of flowering time of bhlh93 mutant compared to GA and vernalization pathways. Thus, bHLH93 might represent a novel transcription factor absolutely required for Arabidopsis thaliana to evolve as a facultative LD plant. bhlh93 mutants also show severe adult phenotype such as shorter stature, curly and darker green leaves, and reduced fertility compared to wild type plants. These results suggest that bHLH93 controls plant stature, fertility and chlorophyll content in Arabidopsis. bHLH93 is expressed in a tissue-specific and developmental stage-dependent manner. bHLH93-YFP protein is localized in the nucleus. bHLH93 homodimerizes in yeast, and it has strong transcription activation activity in yeast. These data suggest that, like other bHLH proteins, bHLH93 may function as a transcriptional regulator in the nucleus controlling gene expression. We have identified floral repressor MAF5 as a major target of bHLH93 to promote flowering in SD. bHLH93 binds to MAF5 promoter element in vivo and in vitro. Other than MAF5, FLC and MAF1-2 are also up-regulated in bhlh93 but at a lower level than MAF5. The activation of multiple floral repressors correlates with bhlh93 flowering phenotype. Taken together, these data suggest that bHLH93 may provide selective advantage for evolution of facultative flowering behavior under varying environmental conditions for reproductive success. / text

Cotton is a very important economical crop in the U.S. and throughout the world. The developments in molecular biology offer new and innovative approaches toward evaluating and understanding genetic mechanisms of important agronomical traits. Bacterial artificial chromosome (BAC) libraries have rapidly become the preferred choice for physical mapping. BAC-derived microsatellite or simple sequence repeats (SSRs) markers facilitate the integration of physical and genetic recombination maps. The first objective in this research was to identify chromosome locations of a set of BAC-derived SSR markers in tetraploid cotton. A total of 192 SSR primer pairs were derived from BAC clones of an Upland cotton (Gossypium hirsutum L.) genetic standard line TM-1. Using deletion analysis method, we assigned 39 markers out of the 192 primer pairs to 18 different chromosomes or chromosome arms. Chromosomal assignment of these markers will help to improve the current cotton genetic linkage maps and facilitate positional candidate gene cloning, comparative genome analysis, and the coordination of chromosome-based genome sequencing projects. Wild race stocks (Gossypium spp.) represent valuable resources for genetic improvement. Most primitive accessions are photoperiod sensitive; they do not flower under the long days of the U.S. cotton belt. Molecular markers were used to locate quantitative trait loci (QTLs) for node of first fruiting branch (NFB), node of first open boll (NOB), and fruiting score (FS). An F2 population consisted of 251 plants from the cross of a day neutral cultivar Deltapine 61, and a photoperiod sensitive accession Texas 701, were used in this study. For each trait, three major QTLs were mapped to chromosome 16, 21, and 25. QTL analysis was also conducted in two F2 populations generated from the cross between Deltapine 61 and two photoperiod sensitive accessions (T1107, PI 607174; T1354, PI 530082) of Upland cotton (G. hirsutum L.). QTL analysis indicated that NFB differed between the two F2 populations. Two major QTLs (q-NFB-c21-1 and q-NFB-c25-1) were found in population 1107; whereas, only one (q-NFB-c25-1) was important in population 1354. Discovering QTLs associated with flowering time may have the potential to facilitate day neutral conversion of wild photoperiod sensitive accessions.

Factors affecting flowering time have been extensively studied for decades. Greater understanding of flowering time has wider implications in agriculture and ecology as the trait is crucial to optimising reproductive success. It is best understood in the genetic model Arabidopsis thaliana (Arabidopsis), in which loss and gain of function mutations have identified several pathways that regulate flowering and its response to the environment. This has been complemented by studies of natural variation in flowering. Worldwide accessions of Arabidopsis have been used to identify additional flowering regulators and to examine the evolution of these genes and their potential involvement in adaptation to different environments. One of the most extensively studied pathways is responsible for accelerated flowering in response to an extended period of cold (vernalization). Several studies have attributed a substantial proportion of worldwide variation to the genes FRIGIDA (FRI) and FLOWERING LOCUS C (FLC), both of which are instrumental in conferring sensitivity to vernalization, though other genes have also been found. This study examines flowering time variation locally in populations of Arabidopsis from in and around Edinburgh. It identifies substantial, genetically determined variation in flowering time and in sensitivity to photoperiod and vernalization between local accessions. Variation in FRI and FLC sequences and in their levels of expression were detected in local accessions, but these were able to explain little of the phenotypic variation observed. Hybrids between local accessions showing extreme differences in flowering time or responses to photoperiod and vernalization were therefore used to map genes underlying their differences as quantitative trait loci (QTL). This analysis identified a locus in chromosome 5 that could account for differences in vernalization sensitivity. This region includes the VERNALIZATION INSENSITIVE 3 (VIN3) gene. Sequence differences between VIN3 alleles and their expression in response to vernalization supported the potential involvement of this gene in local flowering time variation.

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The aim of this study was to elucidate the control of flowering in Protea spp. The main factor that makes studying flowering in this diverse genus so challenging is the fact that most Protea spp. and their commercial hybrids have very dissimilar flowering times. The carbon input into floral organ formation and support is expensive as flowers from Protea spp are arranged in a very large ‘flowerhead’ (50 mm by 130 mm for ‘Carnival’) that can take up to two months to develop fully. Therefore the carbon needed for structural formation, metabolic respiration and the sugar-rich nectar production make these structures extremely expensive to form and maintain. Protea is a sclerophyllous, woody perennial shrub with a seasonal flush growth habit. The leathery leaves (source tissue) produce most of the carbon needed for support and growth of the new leaves, roots and flowers (sink tissue). In the case of expensive structures, such as the inflorescences, remobilization from stored reserves, probably from underground storage systems, can be observed for structural development and maintenance. At all times the flush subtending the apical meristem or florally developing bud provides the largest proportion of carbon for support of the heterotrophic structures. Protea apical meristems stay dormant during the winter months, but BA (benzyl adenine, 6-benzylaminopurine) application to the apical meristem of the Protea hybrid ‘Carnival’ has shown to be effective in the release of dormancy and subsequently shift flowering two months earlier than the natural harvesting time. BA is thought to shift source/sink relationships by stimulating the remobilization of carbon to the resting meristem. Although no direct evidence was found for this in our assay, possible reasons for a weak assay are discussed. This study combined physiological research with the use of molecular tools. An homologue of the Arabidopsis thaliana meristem identity gene, LEAFY, was identified in Proteaceae. PROFL (PROTEA FLORICAULA LEAFY) is expressed in both vegetative and reproductive meristems as well as leaves. PROFL expression in leaves may have an inhibitory effect on vegetative growth, as the expression was high at the same time as the expression in the apical meristem increased marking the transition to reproductive growth. In perennial species such as Protea, the availability of carbon is thought to be the main factor controlling floral development. Possible mechanisms of control may be through the direct control of meristem identity genes such as PROFL through sugar signaling. BA did not have a direct effect on PROFL expression although the expression pattern was one month in advance when compared to the natural system. PROFL expression seems to be consistent with that found for other woody perennial species and would therefore be a convenient marker for floral transition. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die inisiëring van blomvorming in Protea spp. te ondersoek. Die verskil in blomtyd tussen Protea spp. en hul kommersieel ontwikkelde hibriede maak die studie van hierdie genus ‘n groot uitdaging. Die groot hoeveelheid koolstof wat benodig word vir blomvorming in Protea is hoofsaaklik as gevolg van die grootte (50 mm by 130 mm vir ‘Carnival’) van die blomkop waarin individuele blomme geranskik is. Hierdie blomkoppe kan tot 2 maande neem om volwassenheid te bereik. Die koolstof benodig vir strukturele ontwikkeling, metaboliese respirasie en produksie van suiker-ryke nektar maak die vorming van hierdie structure ongelooflik duur. Protea is ‘n bladhoudende, houtagtige bos met ‘n seisoenale groeipatroon. Die leeragtige blare voorsien die grootste hoeveelheid koolstof vir die ontwikkelende blare, wortels en blomme. Koolstof vir die ontwikkeling en ondersteuning van die groot stukture soos die blomkoppe word gedeeltelik deur die huidige fotosinfaat voorsien en bewyse vir die remobilisasie van gestoorde koolstof, heel waarskynlik vanaf ondergrondse stukture, is gevind. Die blare van die stemsegment wat die apikale meristeem of ontwikkelende blom dra, voorsien altyd die grootse hoeveelheid koolhidrate aan die ontwikkelende struktuur. Die apikale meristeme van Protea bly dormant gedurende die winter maande, maar applikasie van BA (bensieladenien, 6-bensielaminopurien) aan die apikale meristeme van die Protea hibried ‘Carnival’ verbreek dormansie en die blomtyd van hierdie gemanipuleerde plante is daarom twee maande vroeër as die natuurlike oestyd. Daar word gespekuleer dat BA applikasie aan die apikale meristeem die hoeveelheid koolstof wat na die dormante meristeem gestuur word verhoog wat dan die dormansie verbreek. Hierdie studie beproef ongelukkig hierdie hipotese swak en redes hiervoor word bespreek. In hierdie studie word fisiologiese analises met molekulêre studies gekombineer. ‘n Meristeem identiteits gene wat homologie wys met LEAFY (LFY) in Arabidopsis thaliana (Arabidopsis), PROFL (PROTEA FLORICAULA LEAFY), is in Proteaceae geïdentifiseer. PROFL word uitgedruk in reproduktiewe meristeme so wel as die vegetatiewe meristeme en blare. PROFL uitdrukking in blare mag dalk ‘n inhiberende effek hê op die vorming van nuwe blare, omdat die uitdrukking hoog was op die selfde tyd as wat blominisiëring plaasgevind het in die apikale meristeem. Die transisie tot reproduktiewe groei word gekenmerk deur ‘n verhoging in PROFL uitdrukking in die apikale meristeem. In meerjarige plante soos Protea spp word daar verwag dat die teenwoordigheid van voldoende koolstof die oorskakeling na reproduktiewe groei inisieer. Dit mag wees deur die direkte aksie van suikers met gene soos PROFL wat die finale skakel na reproduktiewe groei beheer. Alhoewel BA applikasie geen direkte effek gehad het op PROFL uitdrukking nie, was die blomtyd met twee maande vervroeg. PROFL uitdrukking was vergelykbaar met die uitdrukking van LFY homoloë in ander houtagtige, meerjarige plante en kan gebruik word as ‘n merker vir blominisiëring in Protea spp.

published_or_final_version / abstract / toc / Botany / Master / Master of Philosophy

Early flowering is important for maize adaptation to short-season growing environments. Dwarfism, by preventing lodging, has the potential to increase grain yield. This thesis investigates three novel mutants of maize. The early flowering mutant (EarlyF) sheds pollen 1 to 5 days earlier than wild type plants. EarlyF, was shorter and developed fewer leaves than wild type plants, suggesting an earlier transition from vegetative to reproductive development. A candidate QTL for EarlyF maps to bin 7.03. The two allelic dwarf mutants, brachytic3-1 and brachytic3-2, have short internodes at maturity, resulting in severely reduced plant height. Despite being short, days to pollen shed and number of leaves were unchanged for both brachytic3-1 and brachytic3-2. brachytic3 maps to a ~ 7 Megabase region of bin 5.04. This thesis characterizes EarlyF, br3-1 and br3-2 and sets the stage for positionally cloning the mutations causing these mutants and has potential to contribute to maize improvement.

Temperate maize is one of few model species that relies mainly on endogenous indicators of the plant’s developmental stage to cue the onset of reproductive development. The INDETERMINATE1 (ID1) transcription factor is a key regulator of the floral transition and id1 mutants are very late-flowering. ID1 is expressed and remains localized in developing leaves, while florigenic signals originate in mature, photosynthetically active leaves. Since very little is known about the molecular components of the floral transition in maize, and in autonomously flowering species at large, this work utilized id1 mutants to analyze the transcriptional and physiological alterations associated with the floral transition in maize. Analyses of functional categories of transcriptional change between developing leaves of id1 non-flowering mutants and normal flowering maize suggest a role for ID1 in energy metabolism and epigenetic regulation of leaf development. In addition, a novel family of -glucosidase genes were found to be expressed exclusively in immature leaves of normal flowering maize in a pattern similar to the ID1 gene suggesting that these genes may act in concert downstream of ID1. Further, profiling of transcript and metabolite alterations in mature leaves, which are likely the source of floral cues, suggest that coordination of resource storage in the form of transitory starch is an important signal for floral promotion in maize. Finally, analysis of the floral transition in Balsas teosinte, the progenitor of modern maize and an obligate short-day plant, suggests that ID1 may define a regulatory module unique to the autonomous floral regulation pathway in maize and related grass species.

Canada is a global leader in flax production, but flax acreage in Canada remains limited since flax is not well adapted to the northern Prairies. Therefore, breeding early-flowering and early maturing flax cultivars that are adapted to the climate of the northern Prairies is one of the major strategies to expand flax acreage in Canada. The objective of this project is to understand flowering time in flax and generate early flowering genotypes that are adapted to the continental climate of the Canadian Prairies. This project examined photoperiod sensitivity in five Canadian flax cultivars (CDC Sorrel, CDC Bethune, Flanders, Prairie Thunder and Royal) and three M9 genotypes derived from 5-azacytidine (5-azaC) treatment (RE1, RE2 and RE3). To investigate how each cultivar or genotype responds to photoperiod changes, a reciprocal transfer experiment between long day and short day conditions was conducted. All cultivars and genotypes were photoperiod sensitive. However, the level of sensitivity and length of the sensitive phase varied among cultivars and genotypes. The five cultivars were more sensitive to photoperiod changes compared with the three mutant genotypes, while RE2, which was the earliest flowering genotype, was the least sensitive genotype. This project, in addition, examined the expression pattern of ELF4 (EARLY FLOWERING 4), a specific flowering-related gene. This experiment was conducted with three Canadian flax cultivars (CDC Sorrel, CDC Bethune and Royal) and one 5-azaC mutant genotype (RE2). GAPDH (Glyceraldehyde 3-phosphate dehydrogenase) was used as a reference gene in RT-qPCR. Results of RT-qPCR demonstrated that CDC Sorrel and CDC Bethune had a similar expression pattern, while Royal and RE2 had a similar expression pattern. This project also sought to generate early-flowering genotypes by treating CDC Sorrel with 5-azaC as well as to introgress the early-flowering trait from RE genotypes into CDC Sorrel via hybridization. Mutant populations (M2, M3, bulk M3) and hybrid populations (F2, F3, and bulk F3) were grown and evaluated for time to flowering, maturity and height under latitude (53° N) field conditions in 2012 and 2013. 5-azaC treatment did not induce significant differences in flowering or maturity in the CDC Sorrel background. However, the early flowering trait was successfully introgressed into CDC Sorrel background since selected progeny lines flowered significantly earlier than the later flowering CDC Sorrel parental line.

M.Sc. (Botany) / Please refer to full text to view abstract