By Andrew Toh SINGAPORE (Reuters) – A unit of Singapore state investor Temasek Holdings is putting its substantial clout behind an app that eases the pain of booking taxis in Singapore and Malaysia, aiming to expand the service in other busy Southeast Asian cities. Vertex Venture Holdings, a $1.2 billion venture capital firm that focuses on emerging companies and funds in Asia and the United States, said on Tuesday it was leading a group of mostly Malaysian investors putting an unspecified eight-figure sum into smartphone app company GrabTaxi. The app, developed by two Harvard Business School graduates, was launched in Malaysia in 2012 as MyTeksi, and then expanded to Singapore a year later. We clearly see GrabTaxi as one such champion in the making. Booking a taxi is often an arduous task in Singapore, a city state with a population of around 5.4 million and just 28,000 cabs.