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