During meiosis, accurate chromosome segregation relies on the proper interaction 
between homologous chromosomes, including synapsis and recombination. The 
meiotic recombination checkpoint is a quality control mechanism that monitors 
those crucial events. In response to defects in synapsis and/or recombination, 
this checkpoint blocks or delays progression of meiosis, preventing the 
formation of aberrant gametes. Meiotic recombination occurs in the context of 
chromatin and histone modifications, which play crucial roles in the maintenance 
of genomic integrity. Here, we unveil the role of Dot1-dependent histone H3 
methylation at lysine 79 (H3K79me) in this meiotic surveillance mechanism. We 
demonstrate that the meiotic checkpoint function of Dot1 relies on H3K79me 
because, like the dot1 deletion, H3-K79A or H3-K79R mutations suppress the 
checkpoint-imposed meiotic delay of a synapsis-defective zip1 mutant. Moreover, 
by genetically manipulating Dot1 catalytic activity, we find that the status of 
H3K79me modulates the meiotic checkpoint response. We also define the 
phosphorylation events involving activation of the meiotic checkpoint effector 
Mek1 kinase. Dot1 is required for Mek1 autophosphorylation, but not for its 
Mec1/Tel1-dependent phosphorylation. Dot1-dependent H3K79me also promotes Hop1 
activation and its proper distribution along zip1 meiotic chromosomes, at least 
in part, by regulating Pch2 localization. Furthermore, HOP1 overexpression 
bypasses the Dot1 requirement for checkpoint activation. We propose that 
chromatin remodeling resulting from unrepaired meiotic DSBs and/or faulty 
interhomolog interactions allows Dot1-mediated H3K79-me to exclude Pch2 from the 
chromosomes, thus driving localization of Hop1 along chromosome axes and 
enabling Mek1 full activation to trigger downstream responses, such as meiotic 
arrest.