Functional architecture of two exclusively late stage pollen-specific promoters in rice (Oryza sativa L.)

Late stage pollen-specific promoters are important tools in crop molecular breeding. Several such promoters, and their functional motifs, have been well characterized in dicotyledonous plants such as tomato and tobacco. However, knowledge about the functional architecture of such promoters is limited in the monocotyledonous plant rice. Here, pollen-late-stage-promoter 1 (PLP1) and pollen-late-stage-promoter 2 (PLP2) were characterized using a stable transformation system in rice. Histochemical staining showed that the two promoters exclusively drive GUS expression in late-stage pollen grains in rice. 5' deletion analysis revealed that four regions, including the -1159 to -720 and the -352 to -156 regions of PLP1 and the -740 to -557 and the -557 to -339 regions of PLP2, are important in maintaining the activity and specificity of these promoters. Motif mutation analysis indicated that 'AGAAA' and 'CAAT' motifs in the -740 to -557 region of PLP2 act as enhancers in the promoter. Gain of function experiments indicated that the novel TA-rich motif 'TACATAA' and 'TATTCAT' in the core region of the PLP1 and PLP2 promoters is necessary, but not sufficient, for pollen-specific expression in rice. Our results provide evidence that the enhancer motif 'AGAAA' is conserved in the pollen-specific promoters of both monocots and eudicots, but that some functional architecture characteristics are different.