Male sterile 28 encodes an ARGONAUTE family protein essential for male fertility in maize.

Male sterility is a common biological phenomenon in plants and is a useful trait for hybrid seed production. Normal tapetum development is essential for viable pollen generation. Although many genes involved in tapetum differentiation and degradation have been isolated in maize, elements that regulate tapetum development during pollen mother cell (PMC) meiosis are less studied. Here, we characterized a classical male-sterile mutant male sterile 28 (ms28) in maize. The ms28 mutant had a regular male meiosis process, while its tapetum cells showed premature vacuolation at the early meiotic prophase stage. Using map-based cloning, we cloned the Ms28 gene and confirmed its role in male fertility in maize together with two allelic mutants. Ms28 encodes the ARGONAUTE (AGO) family protein ZmAGO5c, and its transcripts primarily accumulate in premeiosis anthers, with more intense signals in PMCs. Transcriptomic analysis revealed that genes related to anther development, cell division, and reproductive structure development processes were differentially expressed between the ms28 mutant and its fertile siblings. Moreover, small RNA (sRNA) sequencing revealed that the small interfering RNA (siRNA) and microRNA (miRNA) abundances were obviously changed in ms28 meiotic anthers, which indicated that Ms28 may regulate tapetal cell development through small RNA-mediated epigenetic regulatory pathways. Taken together, our results shed more light on the functional mechanisms of the early development of the tapetum for male fertility in maize.