Sept 20 (Reuters) - Several U.S. companies, including American Airlines Group Inc (AAL.O), General Motors (GM.N) and Microsoft Corp (MSFT.O), on Monday build on their commitment to clean energy by joining billionaire and Microsoft co-founder Bill Gates" Breakthrough Energy program. The initiative aims to boost development of technologies to achieve the target of net-zero carbon emissions by 2050. Its catalyst program aims to raise money from governments, philanthropists and companies to make capital investments to bring down the cost of clean technology. Bank of America Corp (BAC.N), steelmaker ArcelorMittal SA(MT.LU), Boston Consulting Group (BAC.N) and the philanthropic arm of asset manager BlackRock Inc (BLK.N) have also joined the program, Breakthrough Energy said on Monday. American Airlines said in a statement it has invested $100 million. The program will initially focus on four key areas: direct air capture, green hydrogen, long-duration energy storage and sustainable aviation fuel. The support from U.S. companies comes against the backdrop of President Joe Biden"s plans to accelerate carbon cutting. Earlier this month, the White House said it was targeting 20% lower aviation emissions by 2030. read more