Getting a grip on blast

Csn5 inhibits autophagy by regulating the ubiquitination of Atg6 and Tor to mediate the pathogenicity of Magnaporthe oryzae

Csn5 is subunit 5 of the COP9 signalosome (CSN), but the mechanism by which it strictly controls the pathogenicity of pathogenic fungi through autophagy remains unclear. Here, we found that Csn5 deficiency attenuated pathogenicity and enhanced autophagy in Magnaporthe oryzae. MoCSN5 knockout led to overubiquitination and overdegradation of MoTor (the core protein of the TORC1 complex [target of rapamycin]) thereby promoted autophagy. In addition, we identified MoCsn5 as a new interactor of MoAtg6. Atg6 was found to be ubiquitinated through linkage with lysine 48 (K48) in cells, which is necessary for infection-associated autophagy in pathogenic fungi. K48-ubiquitination of Atg6 enhanced its degradation and thereby inhibited autophagic activity. Our experimental results indicated that MoCsn5 promoted K48-ubiquitination of MoAtg6, which reduced the MoAtg6 protein content and thus inhibited autophagy. Aberrant ubiquitination and autophagy in ΔMocsn5 led to pleiotropic defects in the growth, development, stress resistance, and pathogenicity of M. oryzae. In summary, our study revealed a novel mechanism by which Csn5 regulates autophagy and pathogenicity in rice blast fungus through ubiquitination.

MoVast2 combined with MoVast1 regulates lipid homeostasis and autophagy in Magnaporthe oryzae

Macroautophagy/autophagy is an evolutionarily conserved biological process among eukaryotes that degrades unwanted materials such as protein aggregates, damaged mitochondria and even viruses to maintain cell survival. Our previous studies have demonstrated that MoVast1 acts as an autophagy regulator regulating autophagy, membrane tension, and sterol homeostasis in rice blast fungus. However, the detailed regulatory relationships between autophagy and VASt domain proteins remain unsolved. Here, we identified another VASt domain-containing protein, MoVast2, and further uncovered the regulatory mechanism of MoVast2 in M. oryzae. MoVast2 interacted with MoVast1 and MoAtg8, and colocalized at the PAS and deletion of MoVAST2 results in inappropriate autophagy progress. Through TOR activity analysis, sterols and sphingolipid content detection, we found high sterol accumulation in the ΔMovast2 mutant, whereas this mutant showed low sphingolipids and low activity of both TORC1 and TORC2. In addition, MoVast2 colocalized with MoVast1. The localization of MoVast2 in the MoVAST1 deletion mutant was normal; however, deletion of MoVAST2 leads to mislocalization of MoVast1. Notably, the wide-target lipidomic analyses revealed significant changes in sterols and sphingolipids, the major PM components, in the ΔMovast2 mutant, which was involved in lipid metabolism and autophagic pathways. These findings confirmed that the functions of MoVast1 were regulated by MoVast2, revealing that MoVast2 combined with MoVast1 maintained lipid homeostasis and autophagy balance by regulating TOR activity in M. oryzae.

A slicing mechanism facilitates host entry by plant-pathogenic Phytophthora

Phytophthora species, classified as oomycetes, are among the most destructive plant pathogens worldwide and pose a substantial threat to food security. Plant pathogens have developed various methods to breach the cuticle and walls of plant cells. For example, plant-pathogenic fungi use a 'brute-force' approach by producing a specialized and fortified invasion organ to generate invasive pressures. Unlike in fungi, the biomechanics of host invasion in oomycetes remains poorly understood. Here, using a combination of surface-deformation imaging, molecular-fracture sensors and modelling, we find that Phytophthora infestans, Phytophthora palmivora and Phytophthora capsici slice through the plant surface to gain entry into host tissues. To distinguish this mode of entry from the brute-force approach of fungi that use appressoria, we name this oomycete entry without appressorium formation 'naifu' invasion. Naifu invasion relies on polarized, non-concentric, force generation onto the surface at an oblique angle, which concentrates stresses at the site of invasion to enable surface breaching. Measurements of surface deformations during invasion of artificial substrates reveal a polarized mechanical geometry that we describe using a mathematical model. We confirm that the same mode of entry is used on real hosts. Naifu invasion uses actin-mediated polarity, surface adherence and turgor generation to enable Phytophthora to invade hosts without requiring specialized organs or vast turgor generation.