Male gametophyte specific expression helps identify a conserved gene associated with increased pollen fitness

GRMZM2G372877 was identified as a gene with potential function in the male gametophyte based on its strong expression in mature pollen relative to other maize tissues (Chettoor et al. 2014). Identification of a Ds insertion mutation in this gene from the Brutnell/Vollbrecht collection provided further support for this hypothesis, as initial data indicated the insertion was associated with a male-specific transmission defect. In this study, we confirmed the location of GRMZM2G372877 on chromosome 9, approximately 25 map units away from wx1. We used linkage of the Ds insertion to Wx1+, as well as PCR genotyping, to follow up on the initial results, confirming a male-specific transmission defect from mutant heterozygotes. Because the severity of the transmission defect varied with different crosses (2% to 13%), we tested the idea that the defect decreased pollen fitness when in competition with wild-type pollen. Consistent with this idea, we found that male transmission of the mutation increases in frequency when less pollen is applied to the silk (12% to 43%). Based on DNA sequence, we found GRMZM2G372877 was orthologous to a gene (delegen14) included in a 65-kb deletion associated with the rice no-pollen mutant (Osnop) (Jiang et al 2005), suggesting a conserved function for this gene in pollen. We have tentatively named the gene nop1*, and it encodes a protein with C2 and GRAM domains that are predicted to interact with calcium and phosphoinositides, respectively. Results from microscopy experiments, to visualize specific cellular defects, and to help better determine the function for this gene in pollen or pollen tube development, will also be presente