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Research Project: Molecular Biology of Pollen and Pollen-Pistil Interactions in Crop Plants

Location: Plant Gene Expression Center

Project Number: 2030-21000-037-000-D
Project Type: In-House Appropriated

Start Date: Mar 1, 2013
End Date: Feb 28, 2018

The likelihood of global climate change increases the need for strategies for protecting crop productivity from environmental extremes, including heat, drought, and cold, all of which ultimately impact yield. Pollination and fertilization, in particular, are sensitive to environmental extremes. Pollination and fertilization require an extensive dialog between the tissues of the pistil and the pollen tube. Pollination and fertilization are also model processes for analyzing cell-cell recognition, cell-cell communication and coordination at the molecular, cellular and tissue levels. The long term goal of this project is to identify and characterize the genes and cellular processes that regulate pollen development, pollination, and fertilization, in order to identify genes that can be manipulated to better regulate pollen development, pollination and fertilization. This knowledge will better enable breeders to develop new strategies for genetically hardening these sensitive processes for the field. Genes that are necessary for pollen and sperm function(s) are often evolutionarily conserved and thus identifiable using comparative genomic strategies; such conserved genes are candidates for manipulations across a wide range of plant species. Objective 1: Identify and analyze, at genetic, molecular and protein levels, interactions that occur in pollen development, in pollen-pistil interactions or in sperm-egg interactions that determine the outcomes of these processes. Objective 2: Identify and characterize evolutionarily conserved regions of the genome whose function is to mediate pollen development and/or pollen-pistil interactions. Objective 3: Determine new means to regulate pollen development and pollen-pistil interactions.

Objective 1: We hypothesize that protein complexes composed of receptor kinases and other interacting proteins will mediate cell signaling during pollen tube growth and pollen-pistil interactions. We further hypothesize that the components of the complexes will vary at different stages of pollen tube growth. To test this hypothesis we will use biochemical approaches such as co-immunoprecipitation and yeast two hybrid interactions, and in vivo imaging techniques, such as BiMolecular Fluorescence Complementation, to determine what proteins are present in the complexes at different stages of pollen tube growth, and how and when individual proteins participate in these complexes. These approaches have been successful in our previous studies. It is possible that particular interactions will fail to be confirmed biochemically, either because a third partner is necessary, or because the interaction is weak or transitory. If so, a genetic approach will be used to determine the functions of candidate proteins. Objective 2: We hypothesize that genes that encode pollen-specific proteins whose amino acid sequences are highly conserved across angiosperms will play important roles during pollen function. Conversely, we hypothesize that genes encoding pollen-expressed proteins that exhibit enhanced amino acid variation across angiosperms, or that are family-specific, might contribute to speciation. To test these hypotheses, we will identify candidate genes from RNA-seq analyses and use comparative genomics and multi-sequence alignments to identify conserved (or conversely, highly variable) protein domains. The bioinformatic approach is well-established and robust, but for particular genes it might not prove fruitful. However, since there are many such candidate genes, we anticipate at least partial success. Similarly, demonstrating a critical reproductive function for genes will follow well-established protocols (such as gene knock-outs and phenotypic analyses), but it is likely that some candidates will be excluded because no phenotype will be seen. Objective 3: We hypothesize that manipulating gene expression of key genes will improve stress tolerance during reproduction. To test this hypothesis, we will first establish robust methods for applying transient stresses to growing pollen tubes, then identify genes whose expression changes upon a stress treatment, such as temperature. Genes up-regulated upon stress treatment are candidates for stress tolerance, i.e. overexpressing the gene to higher levels might improve stress tolerance under those stress conditions, while down-regulating such genes (for example, via a gene knockout) is predicted to increase stress sensitivity and would validate the role of the gene in response to stress. Again, as in objective 2, some candidates might not fulfill this goal, but as there are many candidate genes, it is likely that the approach will prove fruitful.