Biotrophic invasive
hyphae (IH) of the
blast fungus Magnaporthe oryzae secrete effectors to alter host defenses and
cellular processes as they successively invade living
rice (Oryza sativa) cells. However, few blast effectors have been identified. Indeed, understanding
fungal and
rice genes contributing to biotrophic invasion has been difficult because so few plant cells have encountered IH at the earliest
infection stages. We developed a robust procedure for isolating infected-rice sheath
RNAs in which approximately 20% of the
RNA originated from IH in first-invaded cells. We analyzed these IH
RNAs relative to control mycelial
RNAs using M. oryzae oligoarrays. With a 10-fold differential expression threshold, we identified known effector PWL2 and 58 candidate effectors. Four of these candidates were confirmed to be
fungal biotrophy-associated
secreted (BAS) proteins. Fluorescently labeled BAS proteins were
secreted into
rice cells in distinct patterns in compatible, but not in incompatible, interactions. BAS1 and BAS2 proteins preferentially accumulated in biotrophic interfacial complexes along with known avirulence effectors, BAS3 showed additional localization near
cell wall crossing points, and BAS4 uniformly outlined growing IH. Analysis of the same infected-tissue
RNAs with
rice oligoarrays identified putative effector-induced
rice susceptibility genes, which are highly enriched for sensor-transduction components rather than typically identified defense response genes.
