Pollen-stigma interactions: events and players that set off the path to reproductive success

Pollination in flowering plants is the requisite process for fertilization. The production of seeds and fruits, preservation of plant species and generating diversity all rely on pollination success. This project focuses on understanding how pollen and stigma, the pollen receptive surface on the pistil (the female reproductive organ) interact to initiate pollination.

The first event on the stigma is for the pollen to germinate, thereby generating a pollen tube which penetrates the stigma and elongates inside the pistil to deliver sperm to the egg. The mechanisms underlying the activation of dormant pollen grains are poorly understood. The process requires the pollen cytoplasm to distribute to a small area where a pollen tube emerges from the grain and grows into the pistil to start a fruitful journey.

This project focuses on obtaining a molecular understanding of these earliest pollination events. Water transfer between the stigma and pollen to activate the pollen grain, cytoplasmic reorganization in the pollen to engineer the tube extrusion and tube growth process, and the enzymes that modify the pollen and stigma cell walls to facilitate tube extrusion and its penetration of the pistil will be examined for their contribution to the success of the early pollination events.

The project will train undergraduates, Master’s, Ph.D. students, and post-graduate level scientists, feeding the pipeline for the research workforce and future leaders in science. A collaboration with Girls Inc. of the Valley (Holyoke MA) will bring high school girls for a summer experience centered on the project research area.

Important advances have been made in recent years in the molecular and cellular understanding of the reproduction process in flowering plants, especially in how the sperm-bearing pollen interact with tissues in the pistil to enable fertilization to produce seeds. Important but under-explored are the earliest events which occur upon pollen landing on the receptive surface of the pistil, the stigma, to set off the pollination process.

This project focuses on obtaining a molecular and cellular understanding of these early events. Specifically, the project explores how the stigmatic papilla cells mobilize water from the stigma to hydrate a dry and dormant pollen grain to activate germination, which involves the extrusion of a polarized outgrowth from the grain and its development into a pollen tube.

It also examines how the pollen grain mobilizes its cell surface signaling and cytoplasmic components to orchestrate pollen tube extrusion and penetration of the stigma. Considerable cell wall degradation and modification activities occur in both the pollen and the pistil to enable the germination and tube growth process. Therefore, how cell wall degradative enzymes contribute to these processes will also be examined.

The research uses Arabidopsis as the model system and relies on combined molecular, transgenic, cell biological and biochemical approaches. The project will provide students from undergraduate to postdoctoral levels with a broad range of scientific knowledge and experience in research approaches that can be broadly applied. A summer workshop related to plant reproduction will be developed for high school students from neighboring inner cities.

The Cellular Dynamics and Function cluster in the Division of Molecular and Cellular Biosciences is co-funding this award.

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.