Research
ANTHEROLOGY
Anthers express the most genes of any plant organ, and their development involves sequential redifferentiation of many cell types to perform distinctive roles from stamen primordia initiation through pollen dispersal. As the source of pollen and thus male gametes, anthers are essential for plant sexual reproduction and are highly conserved in function; however, considerable natural variation exists in the development, physiology, and architecture of anthers depending on the ecology, pollination syndrome, and mating system of each plant species. In addition, plant breeders’ ability to control pollen production underpins hybrid seed production of most crops making understanding male sterility and male fertility a key goal for agricultural improvement. The Marchant Lab utilizes molecular analyses, comparative genomics, and microscopy to investigate fundamental questions regarding plant reproductive biology, development, and evolution, as well as the effects of global climate change on plant fertility.
Anther Diversity and Evolution in the Genomics Era
Anther evolution has been of distinct interest among plant systematists and evolutionary biologists for decades due the diverse architecture, physiology, and development, yet conserved fundamental function in producing and releasing pollen grains. Differences in anther structure were used to characterize flowering plant clades at the family and ordinal levels, leading to an abundance of classic microscopy-based literature on cellular architecture, basic cell type roles, and broad developmental stages. Despite the previous focus on this essential organ, no studies outside of a few model systems (e.g. Arabidopsis, rice, maize) have genetically characterized or implemented modern evolutionary comparisons of anther development, anther-specific genes, or anther cell layers. To remedy this gap in knowledge and significantly broaden our evolutionary understanding of the anther and its predecessors (microsporangia and sporangia), the Marchant Lab is expanding the evolutionary breadth of our genetic analyses by staging developmental series of anthers and sporangia from diverse land plants, ranging from bryophytes to eudicots.
With these data we analyze the gene family evolution of select transcription factors regulating anther development, the conservation or diversity of specific anther cell layers and their functional roles, and discover specific genes related to pollination syndrome (ex. sporopollenin-related genes) or mating system (ex. F-box genes to prevent selfing). The expansion of these analyses beyond just flowering plants will confirm or refute the homology of the cell layers surrounding the germinal cells and similarly provide insight into the genes needed for pollen/spore production. Furthermore, fully understanding the development of specific anther cell layers, the expression patterns and role of the anther in species beyond maize, rice, and Arabidopsis can provide a framework for identifying male-sterility genes in crops lacking substantial genetic resources. Hence, this work has enormous agricultural implications beyond the foundational evolutionary perspective.
Stressed Stamen: How a Changing Climate Influences Anther Development and Reproductive Success
Anther development and pollen production is one of the most environmentally sensitive developmental process in the plant life cycle. Due to the growing concern and deleterious global effects of climate change on plant species, the Marchant Lab is studying the impact of environmental stressors on male fertility in plants. A single day of extreme heat or cold can lead to the disruption of pollen development and cause male sterility in both crops and native plant species; however, the cellular and transcriptional pathways leading to sterility are poorly understood. Our collaborators in the Meyers Lab (Danforth Plant Science Center) found two environmentally-dependent male-sterile maize mutants (dcl5 and ocl4), in which temperature affects the fertility status of the plants. Environmentally-sensitive genotypes have been used extensively in rice production to control male fertility, yet the topic is relatively unstudied in most other crops or native plant species and completely unstudied at the cellular level. The Marchant Lab is delving into the transcriptional effects of environmental stressors on wild-type maize anther development at the cellular level using RNA-seq to identify the specific anther cell layers that are most susceptible to these heat and drought stress and the particular pathways that are expressed during these treatments. Alongside similar analyses on environmentally-dependent mutant genotypes, we will identify genes and pathways that can be buffered, altered, or removed for more reliable maize breeding programs.
Climate, Terrain, and Beyond: Harnessing Digitized Specimens and Niche Models to Explore Plant Diversity, Evolution, and Conservation
Herbaria have been instrumental in demonstrating the importance of natural history museums in the “Big Data” era of science thanks to the digitization of plant specimens. Plant biologists can now incorporate plant specimens spanning hundreds of years from herbaria across the globe into investigations in ecology, evolution, or conservation.
We have worked extensively with natural history museums and the Integrated Digitized Biocollections (iDigBio), the NSF-funded national center for digitizing and aggregating natural history museum specimens, to establish protocols in the utilization of digitized specimens. With these digitized specimen data, we have applied ecological niche modeling to address fundamental questions in plant ecology and genome biology, as well as conservation and the effects of climate change.
With the Missouri Botanical Garden Herbarium’s seven million plant specimens only a quick drive away, the Marchant Lab welcomes any research projects that incorporate our expertise in ecological niche modeling and digitized museum specimens. Such projects can address topics such as the distribution of rare or endemic species, the effects of climate change on plant populations, phenology, or biogeography. The wealth of information underlying these specimens is colossal but finding the best ways to analyze these data will require insights from a variety of fields.
The alternation of generations from diploid sporophyte to haploid gametophyte and back to sporophyte is a central tenet of plant biology. While enormous variation in the longevity, interdependence, and structure of these multicellular life phases exist, the reproductive processes transitioning between them share universal principles. In bryophytes the gametophyte is the dominant life stage and houses the sporophyte; seed plants have a dominant sporophytic life stage while the gametophytes (pollen grains, embryo sac) are reduced to only a few cells and are short-lived. In contrast, ferns have both independent gametophytes and sporophytes, making them the ideal system for analyzing the alternation of generations and reproductive processes, as little is known regarding the genes and expression patterns underlying these massive changes in architecture, organogenesis, and functional role.
Ceratopteris richardii, or C-Fern, is a homosporous fern which can be found in K-12 and undergraduate classrooms across the globe for teaching plant development and the alternation of generations via the “C-Fern Curriculum.” The Marchant Lab is using Ceratopteris to investigate the transcriptional changes accompanying the alternation of generations. Similar analyses are untenable in flowering plants as the gametophytic cells are highly reduced, short-lived, and confined by sporophytic tissue. In contrast, with Ceratopteris we can easily analyze the major stages of sporangium development (pre-meiosis, meiosis, post-meiosis), spores, spore germination and early gametophyte development, gametophyte sexual maturity (antheridia/archegonia development), fertilization, and sporophyte development. With such analyses we assess the shifts between diploid and haploid expression, the genes regulating these momentous changes in plant architecture and organogenesis, and compare such analyses with the few available flowering plant studies at similar developmental stages to determine the genetic conservation of these processes.
Two Phased Ferns: Investigations into the Alternation of Independent Generations
Ecological niche models of Tragopogon allopolyploids and their diploid progenitors.