* Corporate bond market reforms to follow stock market opening * Authorities want to change heavy reliance on bank loans * Regulator to ease approval process, develop securitisation * Government may resume issuing bonds, aiding corporate issues * Legal framework, extent of foreign appetite remain questions By Bernardo Vizcai** June 1 (Reuters) - As Saudi Arabian authorities prepare to open the stock market to direct foreign investment this month, they're laying plans for a fresh set of reforms: measures to expand and energise the corporate debt market. Corporate bond issuance in the kingdom is the most active in the region, but it lags far behind its potential. There have been ** conventional bonds sold in Saudi Arabia since 2013 while issuance of sukuk (Islamic bonds) in all currencies totalled $7.8 billion in 2014, down from $13.5 billion a year earlier, according to data from Zawya, a Thomson Reuters firm.