Application of rice microspore-preferred promoters to manipulate early pollen development in Arabidopsis: a heterologous system.

KEY MESSAGE: Rice microspore-promoters. Based on microarray data analyzed for developing anthers and pollen grains, we identified nine rice microspore-preferred (RMP) genes, designated RMP1 through RMP9. To extend their biotechnological applicability, we then investigated the activity of RMP promoters originating from monocotyledonous rice in a heterologous system of dicotyledonous Arabidopsis. Expression of GUS was significantly induced in transgenic plants from the microspore to the mature pollen stages and was driven by the RMP1, RMP3, RMP4, RMP5, and RMP9 promoters. We found it interesting that, whereas RMP2 and RMP6 directed GUS expression in microspore at the early unicellular and bicellular stages, RMP7 and RMP8 seemed to be expressed at the late tricellular and mature pollen stages. Moreover, GUS was expressed in seven promoters, RMP3 through RMP9, during the seedling stage, in immature leaves, cotyledons, and roots. To confirm microspore-specific expression, we used complementation analysis with an Arabidopsis male-specific gametophytic mutant, sidecar pollen-2 (scp-2), to verify the activity of three promoters. That mutant shows defects in microspore development prior to pollen mitosis I. These results provide strong evidence that the SIDECAR POLLEN gene, driven by RMP promoters, successfully complements the scp-2 mutation, and they strongly suggest that these promoters can potentially be applied for manipulating the expression of target genes at the microspore stage in various species.