Rice ternary MADS protein complexes containing class B MADS heterodimer.

To investigate ternary MADS protein complexes involved in the regulation of floral organ development in rice, we identified MADS proteins interacting with the class B MADS heterodimers, OsMADS16-OsMADS4 and OsMADS16-OsMADS2, using yeast three-hybrid assay. The class B heterodimers interacted with OsMADS6, 7, 8, 14 and 17, which belong to AP1-like, SEP-like or AGL6-like MADS proteins, generating ternary complexes. The entire region of the K and C domains of OsMADS4 was required for the formation of the OsMADS16-OsMADS4-OsMADS6 and OsMADS16-OsMADS4-OsMADS7 ternary complexes. Analysis results of transgenic plants concomitantly suppressing OsMADS4 and OsMADS6, together with the results of previous studies, suggest that the OsMADS16-OsMADS4-OsMADS6 ternary complex plays an important role in floral development, especially lodicule development.