Identification of a genetic element required for spore killing in Neurospora

Abstract

Meiotic drive elements like Spore killer-2 (Sk-2) in Neurospora are transmitted through sexual reproduction to the next generation in a biased manner. Sk-2 achieves this biased transmission through spore killing. Here, we identify rfk-1 as a gene required for the spore killing mechanism. The rfk-1 gene is associated with a 1,481 bp DNA interval (called AH36) near the right border of the 30 cM Sk-2 element, and its deletion eliminates the ability of Sk-2 to kill spores. The rfk-1 gene also appears to be sufficient for spore killing because its insertion into a non-Sk-2 isolate disrupts sexual reproduction after the initiation of meiosis. Although the complete rfk-1 transcript has yet to be defined, our data indicate that rfk-1 encodes a protein of at least 39 amino acids and that rfk-1 has evolved from a partial duplication of gene ncu07086. We also present evidence that rfk-1s location near the right border of Sk-2 is critical for the success of spore killing. Increasing the distance of rfk-1 from the right border of Sk-2 causes it to be inactivated by a genome defense process called meiotic silencing by unpaired DNA (MSUD), adding to accumulating evidence that MSUD exists, at least in part, to protect genomes from meiotic drive.