Rice blast, caused by the pathogenic fungus Magnaporthe oryzae, is one of the most important destructive fungal diseases of rice worldwide [1]. It occurs throughout the growth phase of rice and mainly damages the leaves, stems and panicles of the rice [2]. Due to its economic importance and sophisticated genetic system, this pathogen has become an ideal model fungus for studying the plant-fungal interactions [3]. During infection, M. oryzae invades host cells, adopts a polar growth mode to multiply and spread within host cells [4]. After a period, obvious necrotic disease lesions appear on the host surface, producing large number of spores to continue the infection cycle [5,6]. Like other plant pathogens, conidia play a crucial role in the infection cycle of M. oryzae [7]. When attached to the surface of plant leaves, conidia begin to germinate and form a polarized germ tube, which under appropriate conditions develops into a dome-shaped appressorium at the tip [2,8]. As appressorium develops, glycogen and lipids in the conidia are gradually broken down into glycerol and transfer to the cells, creating a turgor pressure of up to 8 MPa [1,9]. In M. oryzae, intact cell wall integrity is a prerequisite for achieving this process [10]. After the appressorium matures, a penetrating peg emerges at the base to rupture the rice epidermal cells [11]. The septin ring at the base of the appressorium, composed of F-actin and tubulin as well as scaffolding protein septins, is involved in the accumulation of turgor pressures and the development of penetration peg and is therefore essential for the appressorium-mediated plant infection of M. oryzae [12,13]. The organization of F-actin network, the cytoskeleton of the septin ring, was regulated by the small morphogenetic guanosine triphosphatases, and deletion of either of these would result in a disorganized septin ring and mislocalized virulence determinants such as Chm1, and Tea1 [14], suggesting that precise assembly of the septin ring is necessary to ensure proper function of the appressorium and complete pathogenicity of M. oryzae.

Polarized growth, a major characteristic of filamentous fungi that mainly depends on the polar transportation of secretory vesicles, is a prerequisite for fungal growth and development [15,16]. In this process, microtubules served as the first tracks to transport the secretory vesicles to the apex of hypha [17]. Subsequently, the actin cables continue to help the transportation of them to the apical cortex, where the vesicles fused with the plasma membrane for protein secretion [18,19]. Chitin, one of the major components of fungal cell wall synthesized by chitin synthase (CHS), is critical for the hyphal morphology and cell wall integrity of filamentous fungi [20]. Class V chitin synthase, one type of CHS that possesses an N-terminal myosin motor domain, is critical for fungal virulence during plant-fungal interactions [21,22]. During fungal polarized growth, the class V chitin synthase has been transported to the apical cortex at growth region of filamentous fungi by special cargoes using the motors proteins, microtubule, and F-actin [[23], [24], [25]]. In M. oryzae, MoChs6 was identified as a class V chitin synthase and served as a critical fungal virulence factor involved in detoxifying the host-derived reactive oxygen species (ROS) during plant infection [21]. Till now, how this protein was transported to the hypha tip remains largely unclear. Uncovering this transport process would provide new insights into understanding of class V chitin synthase-mediated polar growth and fungal virulence in M. oryzae.

Zinc finger proteins (ZFPs), one of the largest families of transcription factors that have one or more zinc binding finger domains, are crucial for transcriptional activation, protein degradation, cell differentiation and stress resistance in eukaryotes due to their interaction with DNA, RNA and other proteins [26]. In Saccharomyces cerevisiae, the (C2H2)2 zinc finger proteins Msn2 and Msn4 respond to multiple stressors by activating the transcription of stress-related genes [27]. Hot13, a zinc finger protein with a zinc finger CHY domain, is essential for promoting the assembly of small TIM proteins into complexes in mitochondrial intermembrane space in S. cerevisae [28,29]. In Fusarium graminearum, FgChy1 was identified as a zinc finger CHY domain protein to participate in polarized growth, fungal development and full virulence [30]. In Colletotrichum lagenarium, Cmr1 is one of the Zn(II)2Cys6 zinc finger proteins with two C2H2 zinc fingers at the N-terminus, which regulate the transcription of melanin biosynthesis genes. The absence of this gene led to the disruption of the expression of the melanin synthesis genes SCD1 and THR1 during mycelial melanosis [31]. Besides, the zinc finger protein COS1, which contains four multiple adjacent C2H2-type zinc finger domains, functions as a transcriptional regulator to control genes expression during conidiation. The disruption of COS1 resulted in complete loss of conidia and attenuated virulence in M. oryzae [32]. Overall, the zinc finger protein has multiple functions during fungal development, and new studies of these proteins would provide a better understanding of their broader functions during the diverse aspects of development in eukaryotes.

In this study, MoChy1, a CHY-type zinc finger protein homologous to S. cerevisae Hot13, was identified in M. oryzae. Deletion of Mochy1 led to defects on polarized growth, chitin distribution and conidia production. The Mochy1 mutants displayed mislocalized polarisome protein MoSpa2 and chitin synthases MoChs6 in hyphae. During plant infection, Mochy1 mutants impaired the ability to eliminate host-derived ROS, thereby attenuating virulence on host plants. Besides, the Mochy1 mutants also exhibited defects in the microtubule cytoskeleton and septin ring organization during appressorium formation. Nonselective autophagy was also negatively regulated in the Mochy1 mutants. In summary, our results demonstrate that MoChy1 plays an important role in the development and pathogenicity of M. oryzae.