PRK1, a receptor-like kinase of Petunia inflata, is essential for postmeiotic development of pollen

A pollen-expressed gene of Petunia inflata that encodes a receptor-like kinase named PRK1 was previously identified. The extracellular domain of PRK1 contains leucine-rich repeats which have been implicated in protein-protein interactions, and the cytoplasmic domain was found to autophosphorylate on serine and possibly tyrosine. To investigate the function of PRK1 in pollen development, P. inflata plants were transformed with a construct containing the promoter of a pollen-expressed gene of tomato, LAT52, fused to an antisense PRK1 cDNA corresponding to part of the extracellular domain of PRK1. Three transgenic plants were found to each produce approximately equal amounts of normal and aborted pollen. Analysis of the inheritance of the transgene inserts in two of the transgenic plants, ASRK-13 and ASRK-20, to their progeny revealed that certain transgene inserts co segregated with the pollen abortion phenotype. Microscopic examination of the aborted pollen grains showed that their outer wall, the exine, was essentially normal, but that their cytoplasm contained only starch-like granules. Staining of the nuclei of the microspores at different stages of anther development revealed that the microspores of the transgenic plants developed normally until the uninucleate stage. However, in subsequent stages half of the microspores completed mitosis and developed into normal binucleate pollen, but the other half initially remained uninucleate and subsequently lost their nuclei. Analysis of the amounts of PRK1 mRNA and the antisense PRK1 transcript suggested that the pollen abortion phenotype most likely resulted from downregulation of the PRK1 gene by the antisense PRK1 transgene. These results suggest that PRK1 plays an essential role in a signal transduction pathway that mediates postmeiotic development of microspores.