Structure and function of class III pistil-specific extensin-like protein in interspecific reproductive barriers.

The transmitting tissue of the style is the pathway for pollen tube growth to the ovules and has components that function in recognizing and discriminating appropriate pollen genotypes. In Nicotiana tabacum， the class III pistil extensin-like (PELPIII) arabinogalactan protein is essential for the inhibition of N. obtusifolia pollen tube growth. The transmitting tissue-specific (TTS) arabinogalactan protein amino acid sequence and expression pattern is similar to PELPIII， but it facilitates self-pollinated N. tabacum. The TTS and PELPIII arabinogalactan protein can be divided into the less conserved N-terminal (NTD) and the more conserved C-terminal (CTD) domains. This research tested whether the NTD is the key domain in determining PELPIII function in the inhibition of interspecific pollen tube growth. Three variant PELPIII gene constructs were produced where the PELPIII NTD was exchanged with the TTS NTD and a single amino acid change (cysteine to alanine) was introduced into the PELPIII NTD. The PELPIII variants of N. tabacum were tested for activity by measuring the inhibition N. obtusifolia pollen tube growth by using them to complement a 3'UTR RNAi transgenic line with reduced PELPIII mRNA.