Proteins that Regulate Pollen Tube Growth
We have studied two kinds of pollen tube cell wall proteins. The first type is the Leucine-rich extensin chimera (LRX) proteins, which consist of an N-terminal Leucine-rich repeat domain and a C-terminal hydroxyproline-rich extensin domain. These proteins are found in both monocots and dicots, and are encoded by gene families, some members of which are expressed in vegetative tissues and others are expressed in pollen. The pollen-specific proteins appear to be covalently cross-linked within the cell walls of pollen tubes. While searching for pollen LRX-interacting proteins, we discovered pollen-specific RALF peptides (Rapid ALkalinization Factors) that regulate pollen tube growth. RALFs are also encoded by gene families in both monocots and dicots, and appear to be negative regulators of cell wall expansion in both vegetative cells and pollen tubes.