Analyze the relationship between 'Syriza' and 'Alexis Tsipras' within the context of the input sentence.
Options: owned by, chairperson, product/material produced, 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