Proponent is a synonym of upholder.
As nouns the difference between proponent and upholder
is that proponent
is one who supports something; an advocate while upholder
is someone who upholds something.
As an adjective proponent
is making proposals; proposing.
One who supports something; an advocate
* 2012 November 2, Ken Belson, "[http://www.nytimes.com/2012/11/03/sports/new-york-city-marathon-will-not-be-held-sunday.html?hp&_r=0]," New York Times (retrieved 2 November 2012):
- Proponents of the race — notably Mayor Michael R. Bloomberg and Mary Wittenberg, director of the marathon — said the event would provide a needed morale boost, as well as an economic one.
Making proposals; proposing.