Codon-mediated effector secretion by Magnaporthe oryzae in host rice cells

Magnaporthe oryzae, the fungus causing rice blast disease, deploys effectors to manipulate host immunity. Apoplastic effectors are secreted conventionally, whereas cytoplasmic effectors are deployed into the biotrophic interfacial complex (BIC) via the unconventional protein secretion (UPS) pathway. Using reverse genetics and live-cell imaging, we previously showed that the translation of cytoplasmic (but not apoplastic) effector mRNAs relies on efficient decoding of AA-ending codons by the Uba4-dependent thiolation of wobble uridine-34 (s2U34) in cognate tRNAs. Loss of UBA4 abolished cytoplasmic effector secretion. Synonymous AA- to AG-ending codon changes in PWL2 mRNA and (we show here) AVR-Pik mRNA restored cytoplasmic effector production and secretion in Δuba4 strains. In WT, expressing recoded PWL2 or AVR-Pik led to the loss of translational speed control, massive protein production, and super-secretion into the BIC, which destabilized, abolishing infection. In PWL2, mutational analysis shows only one AA-ending codon is required for optimizing translation speed and maintaining BIC integrity, highlighting how codon usage choice on fine scales underpins the success of the M. oryzae-host rice plant interaction. We also show here how cytoplasmic effector secretion from other host-infecting M. oryzae lineages is similarly subjected to Uba4-dependent codon control, indicating it is a conserved, fundamental principle of host infection shaping effector evolution.