The Argyros Family Trust has nominated private-equity investor John Clark to the board of directors of DST Systems Inc., where the trust is the largest shareholder and George Argyros serves as a director.

The Argyros Family Trust and its affiliates own about 21.8% of the Kansas City-based software company, which has a market value of $3.8 billion.

Clark is a managing member of Westar Capital LLC, a Costa Mesa-based private equity firm founded by Argyros, a real estate magnate and philanthropist. Clark and Argyros both serve as directors at Pacific Mercantile Bancorp in Costa Mesa.

The Argyros Family Trust also nominated Janet Kerr, executive director of the Geoffrey H. Palmer Center for Entrepreneurship and the Law at Pepperdine University, to the DST board. She has served as a director at various companies, including Irvine-based retailer Tilly’s Inc. and La-Z-Boy Inc. in Monroe, Mich.

The nominations come as Argyros plans to step down as a director, according a recent filing with the Securities and Exchange Commission.

The Argyros Family Trust and affiliates are “reevaluating [the] investment in DST” and have “identified a number of material deficiencies in matters of corporate governance and stockholder rights,” the filing said.

The family trust notified the DST board of several proposals for consideration, including suggestions to implement a majority-voting standard and to change the structure under which election and term-lengths are determined.