Summary: Rice SVP-group MADS-box proteins, OsMADS22 and
OsMADS55, are negative regulators of brassinosteroid
Shinyoung Lee, Sang Chul Choi and Gynheung An*
Department of Life Science and National Research Laboratory of Plant Functional Genomics, Pohang University of
Science and Technology (POSTECH), Pohang 790-784, Korea
Received 29 September 2007; revised 27 November 2007; accepted 6 December 2007.
*For correspondence (fax +82 54 279 0659; e-mail email@example.com).
Most short vegetative phase (SVP)-group MADS-box genes control meristem identity and flowering time.
Among the three SVP-group genes in rice, OsMADS47 has been reported as a negative regulator of
brassinosteroid (BR) responses. Here, we investigated the functional roles of two close homologs, OsMADS22
and OsMADS55, by generating single, double and triple RNAi lines and overexpression lines. Analyses of the
plants showed that their roles in regulating meristem identity are well conserved; however, the involvement of
these genes in determining flowering time has diversified. Most importantly, OsMADS55 works as a major
negative regulator of BR responses, and OsMADS22 functions to support OsMADS55. Whereas single
OsMADS55 RNAi plants display weak BR responses in the lamina joint (LJ), OsMADS22-OsMADS55 double and
OsMADS22-OsMADS47-OsMADS55 triple RNAi plants manifest dramatic BR responses with regard to LJ
inclination, coleoptile elongation and senescence. Stem elongation is also notably reduced in the double and
triple RNAi plants, probably because of BR oversensitivity. Expression analyses indicate the diversified roles in