3.1 Loss of antitumor activity in an AaLaeAOE26
To clarify the status of A549 cells, the assay was performed with adriamycin as the positive drug. The results found the IC50 of adriamycin against A549 was 2.63 μg/mL, which is consistent with the literature [23]. It showed that the A549 cell line was in normal condition and could be used for the experiment (Fig. 1A). Overexpression of the global regulator AaLaeA in Alternaria alstroemeria led to two contrasting antitumor activities in overexpressed transformants. Among them, the transformantAaLaeA OE29 showed increased antitumor activity [24], while AaLaeA OE26 completely lost its antitumor activity (Fig. 1B). The crude extract of the wild-type strain of A. alstroemeria showed significant inhibition of A549 cells, with the relative inhibition rate in a concentration-dependent manner. At a concentration of 300 μg/mL, the inhibition rate reached 33.43 % and the IC50 value was 328 μg/mL. This indicated that the crude extract of the wild-type strain had a significant inhibitory effect on A549 (Fig. 1B). The insertion site ofAaLaeA OE26 was analyzed via genome resequencing, and the results showed that the insertion site ofAaLaeA OE26 was in the non-coding region. Therefore, we suggest that the insertion of AaLaeA did not destruct other genes (Fig. S1). The data showing the loss of antitumor activity of AaLaeA OE26 was caused by the expression of AaLaeA, and there may be a quantitative-effect relationship between AaLaeA expression and antitumor activity.