Fig. 6.

Model of Nicotiana spp. stylar AGPs and NtPRP evolution. The gray arrow in Fig. 6, indicates an intron introduction into the ancestral AGP and the black arrows show a primary duplication resulting in two genes that subsequently diverged from each other. The diversification occurred primarily in exon I, resulting in size and sequence polymorphisms in IDR1 between PELPIII, 120 K, TTS, and NtPRP. The dashed-line arrows show a duplication of the self- and interspecific-incompatibility gene that lead to 120 K and PELPIII. The dotted-line arrows show a duplication of the gene involved in facilitating pollen tube growth that lead to TTS and NtPRP. Duplication events resulted in subsequent divergence of the four paralogous AGPs that differentiated further, producing AGPs with diverse reproductive functions in regulation of pollen tube growth (processes of II, SI and SC)