You'll need to create a different font that is italicized. If the text object is not published then you can highlight the word in layout and double click the font with italics. When played back from the sequencer this font choice will be maintained.
If your text object is published so that it can be changed from the sequencer; then you need to apply the font in the Template Data tab in the sequencer item. Just put your cursor before the word you want in italics and click the icon with the "aA" above the text.. This will open a dialog where you can choose a font.. You'll see it applies a font tag into the text to indicate the desired font.
#XPression