Take context from the input text and decide on the accurate relationship between 'Syriza' and 'Alexis Tsipras' from the options provided.
Options: product/material produced, chairperson, owned by, distributed by

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