Regulates positively reproductive function by facilitating male gametophyte formation and double fertilization. Mostly expressed in pollen and open flowers and, to a lower extent, in closed flowers. During male gametophyte development, first observed in bicellular pollen, and accumulates gradually during pollen maturation in tricellular pollen and mature pollen. Altered male gametophytic development with frequent single-fertilization events leading to reduced seed set due to undeveloped ovules. Increased levels of ARI14 in sperm. Transcripts of KPL and ARI14, encoded by adjacent genes organized in a reverse orientation, have the potential to generate natural cis-antisense siRNAs (cis-nat-siRNAs) pair targeting ARI14 in sperm, thus leading to opposite expression levels during male gametophyte development.