The three, who were staunch government critics, face life in prison if found guilty of charges that also crimes against the state and membership in Gulen's movement, which Turkey has branded a "terrorist" organization.
Ilicak and the Altan brothers are among six jailed defendants. Ten other suspects, including Ekrem Dumanli, the former editor-in-chief of the Gulen-linked Zaman newspaper, are at large and being tried in absentia. Another defendant is free pending the verdict.
The media advocacy group Reporters Without Borders called for the immediate release of Ilicak and the Altan brothers, who have been in pre-trial detention since July and September. "It is high time that the Turkish authorities ended their systematic criminalization of critics," the group said. "The already worrying situation of its media has become critical under the state of emergency proclaimed after the 2016 coup attempt."
Turkey has arrested some 50,000 people in a massive crackdown following the failed coup and dismissed tens of thousands of other people from government jobs. Around 150 media organizations have been closed down and more than 100 journalists have been jailed.
Gulen, who is in self-imposed exile in the United States, has denied involvement in the coup attempt.