Diversification of SEPALLATA genes in grasses

SIMON T. MALCOMBER; REINHEIMER RENATA; ELIZABETH A. KELLOGG

Congreso; 48th Annual Maize Genetics Conference; 2005

Members of the SEPALLATA (SEP) family of MIKC-type MADS-box genes exhibit distinct patterns of expression in rice and maize and have been linked to both the origin and diversification of the grass spikelet. To better understand the evolution of SEP genes in grasses we have isolated orthologues of the five rice SEP genes LEAFY HULL STERILE1 (LHS1), Oryza sativa MADS5 (OsMADS5), OsMADS7, OsMADS8 and OsMADS34 from 12 phylogenetically disparate grass species. Phylogenetic analysis of 120 SEP genes from diverse flowering plants indicates that only OsMADS7 and OsMADS8 are demonstrably orthologous to an Arabidopsis SEP gene; the remaining three grass SEP genes are restricted to monocots. Using a combination of RT-PCR and in situ hybridization, we document diverse patterns of gene expression. All grass SEP genes are detected in inflorescence tissue, but at least one SEP gene is also detected in root, culm and leaf tissue in each of the sampled species. The identity of the widely expressed SEP gene differs from species to species. Using in situ hybridization, we show that LHS1 is expressed in several of the upper florets of Eleusine indica (yard grass) spikelets, but only in the upper floret of Panicum maximum (guinea grass) spikelets. These data confirm our earlier observation that LHS1 may act as a selector gene (specifying the terminal floret of the spikelet) only in species with basipetal maturation of the florets. OsMADS5 is expressed in the palea and lemma of several florets of the spikelet in oats, barley, Chasmanthium (sea oats) and sorghum, but is expressed only in the stamens and pistil in rice. These heterogeneous patterns of expression support the hypothesis that SEP genes have diversified extensively in grasses and may have different roles in different species.