Summary
The activation and developmental regulation of the promoter of the tomato late pollen gene lat52 was analysed in Nicotiana tabacum and Arabidopsis thaliana to investigate the conservation of regulatory mechanisms in species with bicellular and tricellular pollen. Promoter activity in transgenic plants containing the lat52 promoter fused to the β-glucuronidase (gus) gene was studied in detail throughout pollen development by fluorimetric and histochemical analysis of GUS activity, and by RNA analysis. These studies showed that in transgenic A. thaliana the lat52 promoter was activated in late uninucleate microspores immediately prior to microspore mitosis, whereas in transgenic N. tabacum lat52 promoter activity was first detectable immediately following microspore mitosis in young bicellular pollen grains. Thus, the precise activation of the lat52 promoter was not strictly dependent on passage through microspore mitosis in A. thaliana. Despite this temporal difference, the pattern of lat52 promoter activity during vegetative cell maturation showed a very similar cumulative pattern of activity in both species, which was correlated with a similar accumulation of gus transcript and spore protein content. Furthermore, the expression of a lat52 promoter directed nuclear-targeted β-glucuronidase fusion protein allowed lat52 promoter activity to be localized specifically to the vegetative cell during pollen development in A. thaliana.