In general italic Arabidopsis thaliana is used (when both genus and species) .What we should prefer either normal Arabidopsis or italic Arabidopsis within manuscript where only genus mentioned?
brief discussion in below article:
http://www.globalsciencebooks.info/Online/GSBOnline/images/2012/AAJPSB_6(SI1)/AAJPSB_6(SI1)118-120o.pdf
some good articles used normal and others italic Arabidopsis.