MAGO proteins safeguard the plant male germline under environmental stress

Although plants are able to withstand a range of environmental conditions, spikes in ambient temperature can impact on crop fertility, causing significant economic loss – a problem exacerbated by climate change. It is therefore important to understand the molecular mechanisms by which the environment affects plant fertility. Here, we identified two Argonaute-like proteins whose activities are required for male fertility in heat-stressed maize plants. MALE-ASSOCIATED ARGONAUTE 1 and 2 (MAGO1 and MAGO2) associate with heat-induced phased secondary small RNAs in pre-meiotic anthers, which control the activity of retrotransposons in male germ cells. Biochemical and structural analyses revealed how MAGO2 activity and its interaction with retrotransposon RNA targets is modulated through the dynamic phosphorylation of a set of highly conserved surface-located serine residues. Collectively, our findings reveal an RNA-guided surveillance mechanism that controls the activity of retrotransposons in male germ cells, which is vital to sustain maize fertility under environmental stress conditions.