Abstract
Fusarium oxysporum exhibits conidial anastomosis tube (CAT) fusion during colony initiation to form networks of conidial germlings. Here we determined the optimal culture conditions for this fungus to undergo CAT fusion between microconidia in liquid medium. Extensive high resolution, confocal live-cell imaging was performed to characterise the different stages of CAT fusion, using genetically encoded fluorescent labelling and vital fluorescent organelle stains. CAT homing and fusion were found to be dependent on adhesion to the surface, in contrast to germ tube development which occurs in the absence of adhesion. Staining with fluorescently labelled concanavalin A indicated that the cell wall composition of CATs differs from that of microconidia and germ tubes. The movement of nuclei, mitochondria, vacuoles and lipid droplets through fused germlings was observed by live-cell imaging.
Highlights
Conidial anastomosis tubes (CATs) are distinct types of cell protrusions that are different from germ tubes (GTs)
In 1% Potato dextrose broth (PDB) supplemented with NaNO3 a few microconidia started to form germ tubes before adhesion took place, but most germ tubes were formed after adhesion had occurred
CAT fusion did not occur in 1% PDB in the presence of NH4NO3 or (NH4)2SO4, even though adhesion and 80–90% germination had occurred in media containing these supplements (Fig 1)
Summary
Conidial anastomosis tubes (CATs) are distinct types of cell protrusions that are different from germ tubes (GTs). CAT fusion is believed to promote the transport of water and nutrients, which are commonly distributed heterogeneously within the natural environment [2]. Evidence has been obtained that CAT fusion can facilitate horizontal gene transfer between strains to promote genetic variation [3]. The genome possesses supernumerary chromosomes, which are thought to have been acquired by horizontal transfer during evolution [7]. Such studies have revealed the versatile nature of the F. oxysporum genome, which is prone to gene transfer events leading to genetic variation within the species [8].
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