Board Thread:Theories and Speculation/@comment-3001903-20160420024250/@comment-26773508-20160420170356

Sage Mode might boost the dojutsu to a limited extent. During Sasuke vs Itachi, Itachi used a watered-down Tsukuyomi on Sasuke. Sasuke apparently used his Cursed Seal (which basically taps into Nature Chakra to a limited extent) to boost his sharingan and overcome Tsukuyomi. I don't know if this is what actually happened. It could be that Sasuke using the Cursed Seal was only a part of the genjutsu. If Sasuke really used the Cursed Seal in reality and not in genjutsu, then it could be an evidence of Senjutsu boosting the sharingan.