Phytomonas serpens are flagellates in the family Trypanosomatidae that parasitise the tomato plant (
Solanum
lycopersicum L.
), which results in fruits with low commercial value. The tomato glycoalkaloid tomatine and its
aglycone tomatidine inhibit the growth of
P. serpens in axenic cultures. Tomatine, like many other saponins, induces
permeabilisation of the cell membrane and a loss of cell content, including the cytosolic enzyme pyruvate kinase. In
contrast, tomatidine does not cause permeabilisation of membranes, but instead provokes morphological changes,
including vacuolisation.
Phytomonas treated with tomatidine show an increased accumulation of labelled neutral
lipids (BODYPY-palmitic), a notable decrease in the amount of C
24-alkylated sterols and an increase in zymosterol
content. These results are consistent with the inhibition of 24-sterol methyltransferase (SMT), which is an important
enzyme that is responsible for the methylation of sterols at the 24 position. We propose that the main target of tomatidine
is the sterols biosynthetic pathway, specifically, inhibition of the 24-SMT. Altogether, the results obtained in
the present paper suggest a more general effect of alkaloids in trypanosomatids, which opens potential therapeutic
possibilities for the treatment of the diseases caused by these pathogens.
