Plant Anthers

The goal of the proposed work is to understand the regulation of developmental events in anther ontogeny by:

1. organizing hierarchies of gene expression in individual anther cell types and
2. elucidating functions of small RNAs, particularly two unusual classes of phased secondary small RNAs (phasiRNAs) that are highly enriched in grass anthers.

These phasiRNAs are processed from an extensive set of coordinately-expressed long non-coding RNA precursors into secondary small RNAs of 21 or 24 nucleotides. Using precisely staged maize anthers and laser microdissected cell types the project will generate copious transcriptomic and proteomic data, organize transcriptional hierarchies by conducting ChIP-seq of transcription factors, generate extensive data on small RNAs in a spatiotemporal context, and analyze the function and biogenesis of phasiRNAs.

Genetic analysis using existing and engineered mutations will be used to test for essential roles of key transcription and phasiRNA biogenesis factors in anther development. Genetic and omics experiments will test new hypotheses about phasiRNA functions in anther cells and in meiosis.

Our motivation comes from our identification of the phasiRNAs, elucidation of their dynamic expression and that of genes important for their biogenesis is unique to grass flowers, and a set of significant unsolved questions in cell differentiation for meiosis.

One hypothesis is that the long non-coding RNA precursors or the phasiRNAs have signaling roles during both cell fate setting and also participate in chromosome remodeling prior to meiosis.

Most analysis will be conducted in maize because of its exquisite developmental regularity, the large size and ease of anther dissection, and existing molecular and genetic knowledge about maize anthers.

Key insights will be evaluated in rice to distinguish general and species-specific points, with additional comparisons to other grasses.

_{Normal tapetal cells in dcl5-1//Dcl5 siblings (panel A) are densely packed with dark staining materials, which fail to accumulate in the dcl5-1 mutants (panel B).}

This project is a continuation of an earlier, successful project focused on maize pollen fertility and anther development (NSF award 1649424). The team of investigators is highly experienced in anther development, maize and rice genetics and genomics, RNA and chromatin, whole-genome analyses, and computational approaches for analyzing and displaying these data.

The project will build on resources, technologies, and genetic stocks that were developed or are underway from our previous NSF-funded work, and integrate new approaches in imaging, developmental and molecular analysis, genomics, and bioinformatics.

The fundamental questions to be addressed are:

• What are the spatial and temporal accumulation patterns of mRNA and proteins in anther lobe cell types? In particular, how do pre-meiotic and meiotic cells differ from the soma?
• Which transcription factors guide the transitions required for cell fate setting and differentiation of cell type-specific properties during anther development?
• What are the origins and functions of the non-coding phasiRNAs that are specifically expressed in grass inflorescences?

_{Mutant dcl1-5//Dcl1-5 anther development is temperature sensitive}

Together, maize and rice feed over half of humanity and are also the two species studied by these PIs. New information from this project will provide insights into the coordination of anther development and underlying cellular processes, including cellular remodeling, as plant cells switch from mitosis to meiosis.

New insights and resources of broad utility should ultimately contribute to controlling plant fertility in agriculture, particularly in the cereal crops.

The project builds and improves on the varied and extensive outreach and education components of the PIs and their contributions via scientific leadership to continue a strong, positive impact on local and scientific communities, and on the next generation of scientists. The laboratories working on this project offer numerous undergraduate- and graduate-student focused projects – please contact the co-PIs if you’re interested in working on the team.