The MALE STERILITY1 gene of Arabidopsis, encoding a nuclear protein with a PHD-finger motif, is expressed in tapetal cells and is required for pollen maturation

We identified the Arabidopsis MALE STERILITY1 (MS1) gene by transposon-mediated mutagenesis. In the transposon-inserted allele ms1-8, normal immature microspores separated from tetrads, but their subsequent maturation was abnormal: the outer layer of the microspore was absent, and both the microspore and the tapetal layer gradually became vacuolated. Empty locules resulted. The MS1 gene was expressed only in the tapetal layer during a very short period when the microspores were packed as tetrads. By the time the microspores had separated, the gene was no longer expressed. MS1 was not expressed in microspores. MS1 encodes a protein with a PHD-finger motif characteristic of some transcriptional regulators. A fusion protein consisting of the N-terminus of MS1 and green fluorescent protein was localized in the nucleus. These results suggest that MS1 protein is a nuclear signal molecule indispensable for pollen maturation.