**4. Conclusions**

In this study, the WB-formation protein MrHex1 was characterized in the insect pathogenic fungus *M. robertsii*. Unexpectedly, we first found the substantial length variation among Hex1 proteins from different fungi but each with a highly conserved C-terminal tail and the characteristic PTS1 sorting signature. Taken together with the finding that MrHex1 is similarly required for WB formation in *M. robertsii*, the data sugges<sup>t</sup> that the length variation of Hex1 proteins might have no hindrance for their similar functions in WB formation in different fungi. However, phenotypic alterations were clearly evident between Δ*MrHex1* and *Hex1* null mutants of other fungi. In particular, unlike other fungal mutants [18,19], Δ*Mrhex1* demonstrated an equal tolerance to different stress conditions like the WT and Comp of *M. robertsii*. This kind of phenotypic and functional divergence of *Hex1* genes implies the necessity of investigating evolutionarily conserved genes in different fungal pathotypes. The finding that MrHex1 is required in *M. robertsii* for infection structure formation and the topical infection of insect hosts advances our understanding of the control and evolution of fungal entomopathogenicity. Future efforts are still required to investigate the mature type of Hex1 within fungal cells, the relationship between gene positioning and function, and the feasibility of functional complementation of the length-varied Hex1 among different fungi.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2309-608X/6/3/172/s1, Table S1: Characteristics of the Hex1 proteins retrieved from different fungal species.

**Author Contributions:** G.T. and Y.S. performed the experiments and data analysis; S.L. performed insect bioassays; G.T. and Y.S. drafted the manuscript; C.W. designed the experiments, performed bioinformatic analysis, managed the project and finalized the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the National Key R&D Programs of China (2017YFD0200402 and 2018YFA0900502) and the Chinese Academy of Sciences (QYZDJ-SSW-SMC028).

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
