Collaborative Research: Hormonal control of stamen filament growth

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

In both plants and animals, many organs undergo spurts of rapid growth as they develop. Many flower organs grow very quickly for a brief period as flowers open. For successful reproduction, such growth must be coordinated so as to place male and female organs appropriately for pollination, and pollen release needs to occur at an optimal time. This project is to study how plant hormones stimulate rapid growth in stamens, the male flower organs that produce pollen. In many self-pollinating plants, stamen filaments elongate as flowers open to place pollen-bearing anthers near the female stigma. The timing and extent of filament growth thus determines the efficiency of fertilization and seed production, and is important for crop breeding and yield. The project will examine cellular and molecular events during stamen filament elongation in a model plant, to reveal in detail how stamens grow quickly without buckling, how hormones control this growth, and how filament growth is coordinated with pollen release. Genetic tools generated in the work may enable targeted modification of growth in flower organs, for example to modulate the location and timing of pollen release in crop plants. The mechanisms discovered will also be relevant to modulating growth in other organs such as leaves or fruits. Undergraduate students will be introduced to methods of scientific inquiry through carrying out research projects both in courses and in the research labs. Public outreach through museums and campus events will include information on plant reproduction. The project is to study how hormone response pathways control very fast but transient stamen filament growth in the model plant Arabidopsis thaliana. Two auxin response transcription factors, ARF6 and ARF8, mediate growth responses to the hormone auxin, and stimulate stamen filament elongation just before flowers open. ARF6 and ARF8 also stimulate production of another hormone, jasmonate, which further amplifies filament growth rate, and also promotes differentiation needed for anther dehiscence (pollen release). Time-lapse confocal microscopy, single-nucleus RNA-Seq, and fluorescent reporter genes for selected vascular cell types will be used to reconstruct three-dimensional cellular anatomy, growth, and differentiation in rapidly growing stamen filaments. Comparisons of wild type and mutants with decreased or increased hormone responses and filament growth will provide insight into how the hormones act. Biophysical, hormonal, and genetic manipulations, together with jasmonate pathway reporter genes, will probe mechanisms that couple filament growth with the contemporaneous burst of jasmonate production needed for anther dehiscence. Yeast and plant protoplast gene expression systems will be used to identify mutant forms of ARF6 and ARF8 that can activate transcription independently of auxin regulation. Such auxin-independent mutations will then be engineered into Arabidopsis plants to reveal the role of auxin response in flower maturation and other processes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.