Maize <i>rough endosperm6</i> is a predicted RNA helicase required for miRNA processing and endosperm cell patterning

Molecular genetic analysis of maize (Zea mays) rough endosperm mutants has identified multiple RNA processing proteins critical to endosperm development. Here, we report that rough endosperm6 (rgh6) encodes a predicted DEAD-box RNA helicase required for miRNA processing. Mutant rgh6 kernels show reduced grain-fill and increased relative transcript levels of markers specific to proliferating cells as well as epidermal endosperm cell types. Seed genetic mosaics from crosses with the TB-5Sc B-A reciprocal translocation of the short arm of chromosome 5 with a supernumerary B chromosome revealed that rgh6 mutant endosperm inhibits normal Rgh6 embryo development. We mapped the rgh6 locus to a 3-gene interval and confirmed it encodes a predicted DEAD-box RNA helicase with 2 independent transposon-tagged alleles. Transiently expressed RGH6-green fluorescent protein localized to the nucleolus and nuclear speckles, consistent with a function in nuclear RNA processing. Mutant rgh6 endosperms had increased precursor miRNA and decreased mature miRNA levels, indicating that rgh6 affects miRNA processing. Our study demonstrates that precursor miRNA processing and miRNA target regulation are required for normal endosperm development.