A. All three rice MIKC*-type genes are specifically expressed in pollen; B. The rice MIKC*-type proteins form strong heterodimeric complexes between members of the P- and S-clade; C. The rice MIKC*-type heterodimers specifically bind to N10-type CArG-boxes in vitro; D. The rice MIKC*-type heterodimers regulate the expression of downstream genes
In seed plants the MIKCC type shows considerable diversity, but the MIKC* type has only two subgroups, P- and S-clade, which show conserved expression in the gametophyte. Since mutant analyses have been carried out only in the higher eudicot Arabidopsis thaliana so far, the degree of functional conservation of MIKC*-type genes remains to be illuminated. Dr. Zheng Meng's group functionally characterized all three rice (Oryza sativa) MIKC*-type genes, comprising MADS62 and MADS63 from the S-clade and MADS68 from the P-clade. All three genes are specifically expressed late in pollen development, and P- and S-clade genes are not functionally redundant and both clades are indispensable for pollen performance. The rice MIKC*-type proteins form strong heterodimeric complexes solely with partners from the other subclade; these complexes specifically bind to N10-type CArG-boxes in vitro and regulate downstream gene expression by binding to N10-type promoter motifs. These data indicate that the function of heterodimeric MIKC*-type protein complexes in pollen development has been conserved since the divergence of monocots and eudicots, roughly 150 million years ago.