Proposed role of Htf1 in M. oryzae, F. graminearum, F. verticillioides and F. oxysporum.

(A) MoHtf1 is important for proper conidiophore development and subsequent conidia formation. (B) In three Fusarium species, Htf1 plays a critical role in proper development of phialides. HTF1 gene deletion led to aberrant terminal phialide and ultimately abolished macroconidia formation from conidiophores. Macroconidia formation directly from hyphae were also affected, namely in foot cell development. (C) In F. verticillioides ΔFvhtf1 mutants, prototypical microconidia chain and false heads were not observed but rather a 2- to 5- microconidia complex at the apex of monophialides resulting in a floral petal-like shape. This suggests that FvHtf1 is important for basipetal division typically observed in the wild-type F. verticillioides. (D) In F. oxsporum ΔFohtf1 mutants, we observed floral petal-shaped microconidia false head similar to F. verticillioides ΔFvhtf1 mutants suggesting FoHtf1 is important for phialide development and subsequent microconidiogenesis. However, it is not involved in chlamydospore development. c, conidia; cp, conidiophore; ma, macroconidia; tp, terminal phialide; ip, intercalary phialide; fc, foot cell; ch, chain; mp, monophialide; fh, false head; pe, petal; cs, chlamydospore.