Castaner, a Socialist who joined Macron's movement past year, said "our political background will not prevent us to work smartly for France".
More than 20 French media organizations signed an open letter to Macron on Thursday night to express their concerns. Before their meeting, Macron said he wants a Europe that is both more conducive to investment and more protective of workers.
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Macron also suggested he would press on with his ambitious agenda to reform France's rigid labor market and modernize the social security system despite the fierce resistance he is likely to meet.
Gerard Collomb has been a prominent Socialist since becoming mayor of Lyon, France's third biggest city, in 2001.
France's new foreign minister, Jean-Yves Le Drian (John-Eve Le DREE-on), has vowed to promote the country's "key role" in the global community.
A newcomer to global diplomacy, Macron has assumed control of a nuclear power with a permanent seat on the U.N. Security Council as crises persist in Syria, Libya and North Korea.
Le Drian says he expects France to play a crucial role in a "complex, fragile, unstable worldwide situation".
Germany's foreign minister quickly welcomed Le Drian, describing him as someone of "enormous political experience and great renown".
Newly elected French President Emmanuel Macron unveiled his Cabinet with women filling half of the 22 positions.
Macron on Monday named center-right politician Edouard Philippe of the Republicans as his Prime Minister.
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Le Maire is also a leader of the pro-Macron faction in the Republican party.
Viard pointed out that the French society should be inspired by having a young centrist president and a prime minister not well-known in the political circles, adding that people would have a sentiment that Macron was "opening doors and windows closed before". To that end, Nicolas Hulot, a popular environmentalist, was named as ecology minister, a job that includes overseeing energy matters.Hulot, a former TV presenter and one of France's best-known ecologists, has been critical of nuclear energy though not an ardent anti-nuclear campaigner.Shares in state-controlled utility EDF, which produces mostly nuclear power, closed down 6.5 percent on the news.There are a total of 18 ministers.
Last week, the new party announced "a list of 428 candidates for June's elections, half of whom were women", the broadcaster says. If he falls short, the new parliament could vote down Macron's cabinet and choose its own government, sidelining the president.
On the list was Sylvie Goulard, a centrist European Union lawmaker, in charge of defense affairs, Agnes Buzyn, solidarity and health minister and Muriel Penicaud, the minister in charge of managing the thorny employment issue.
In addition, Richard Ferrand, secretary general of Macron's La Republique En Marche!
Jean-Yves Le Drian, 69, who led France's military operations overseas as former President Francois Hollande's defense minister, will stay on in Macron's government as foreign minister and also be in charge of European affairs.
Outgoing defence minister Jean-Yves Le Drian, a Socialist, may keep his post to ensure continuity in French military operations against Islamic extremists in Syria, Iraq and Africa.
The 52-year-old Goulard, the new defense minister, is a pro-European centrist politician.
Macron flew to Berlin in his first full day in office on Monday for talks with Chancellor Angela Merkel over how to inject new life into the Franco-German relationship and the troubled European project.
However, 21 LR members of parliament, including some party heavyweights and former ministers, issued a joint statement urging the party to positively respond to the "hand extended by the president".
Macron has pledged to fight corruption after tax evasion and other scandals hit the previous government.