Hi Lu

I searched for issue tracker plugins for Totara  and only found one that looked outdated.

This community site is an example of what can be done to link Totara to other systems.

The top menus can be linked to the tracker system and relevant menus displayed based on audience rules.

The systems can be connected through Totara authentication plugin such as LDAP that allows Single signon and some data exchange.

If you look on the partners menu in the community site there is a link to  the Issue tracker (JIRA). The data shown here is pulled from JIRA by filters by Partner - the partner is an organisation in Totara and in JIRA. 

The two systems are independent with common signon and links to appropriate menus in Totara

Regards