Abstract
Reactive oxygen species (ROS) are involved in many important processes, including the growth, development, and responses to the environments, in rice (Oryza sativa) and Magnaporthe oryzae. Although ROS are known to be critical components in rice–M. oryzae interactions, their regulations and pathways have not yet been completely revealed. Recent studies have provided fascinating insights into the intricate physiological redox balance in rice–M. oryzae interactions. In M. oryzae, ROS accumulation is required for the appressorium formation and penetration. However, once inside the rice cells, M. oryzae must scavenge the host-derived ROS to spread invasive hyphae. On the other side, ROS play key roles in rice against M. oryzae. It has been known that, upon perception of M. oryzae, rice plants modulate their activities of ROS generating and scavenging enzymes, mainly on NADPH oxidase OsRbohB, by different signaling pathways to accumulate ROS against rice blast. By contrast, the M. oryzae virulent strains are capable of suppressing ROS accumulation and attenuating rice blast resistance by the secretion of effectors, such as AvrPii and AvrPiz-t. These results suggest that ROS generation and scavenging of ROS are tightly controlled by different pathways in both M. oryzae and rice during rice blast. In this review, the most recent advances in the understanding of the regulatory mechanisms of ROS accumulation and signaling during rice–M. oryzae interaction are summarized.
Highlights
Reactive oxygen species (ROS) are highly reactive reduced forms of oxygen molecules, including superoxide (O2− ), hydrogen peroxide (H2 O2 ), hydroxyl radical (OH− ), and singlet oxygen (O2 ) [1,2,3,4,5,6]
ROS play important roles in both the first line of defense termed as pathogen-associated molecular patterns (PAMPs) triggered immunity (PTI) and the second line of defense related to effector-triggered immunity (ETI) [2,6,9,14,46,47,48]
It is known that M. oryzae needs an intricate ROS accumulation during the appressorium formation and penetration, as well as the neutralization of host-derived ROS during in planta growth
Summary
ROS are highly reactive reduced forms of oxygen molecules, including superoxide (O2− ), hydrogen peroxide (H2 O2 ), hydroxyl radical (OH− ), and singlet oxygen (O2 ) [1,2,3,4,5,6]. ROS Accumulations are Required for Infection Structure Formation and Penetration in M. oryzae. 6 transcriptional regulator, Tpc, to regulate the expression of the orthologue of the P22 to control the elongation of the penetration peg Both Nox and Nox interact with small GTPase, subunit (NOXD) of the NADPH oxidase complex. NoxR-Nox NADPH oxidase complex is required for the maintenance of the F-actin network and septin-dependent assembly of the exocyst at the appressorium pore to initiate plant infection. ROS accumulation is required for functional appressorium formation and penetration in M. oryzae. Once inside the rice cells, M. oryzae requires effective anti-oxidant defense systems to scavenge or detoxify the host-derived ROS to spread invasive hyphae by making a conclusion of the phenotypes of many mutants. Further elucidations of these mutants will provide important clues to understand the ROS generating and signaling in the virulent rice–M. oryzae interaction
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