Refer to the input text as context and select the correct relationship between 'Syriza' and 'Alexis Tsipras' from the available options.
Options: product/material produced, owned by, distributed by, chairperson

But prime minister Alexis Tsipras will have to fight down a rebellion in his Leftist Syriza party, a week after more than 38 of his MPs rejected a raft of tax hikes and pension cuts .
chairperson