SUPERWOMAN1 and DROOPING LEAFgenes control floral organ identity in rice

Abstract

We analyzed recessive mutants of two homeotic genes in rice, SUPERWOMAN1 (SPW1) and DROOPING LEAF (DL). The homeotic mutation spw1 transforms stamens and lodicules into carpels and palea-like organs, respectively. Two spw1 alleles, spw1-1 and spw1-2, show the same floral phenotype and did not affect vegetative development. We show that SPW1 is a rice APETALA3 homolog, OsMADS16. In contrast, two strong alleles of the dl locus, drooping leafsuperman1 (dl-sup1) and drooping leaf-superman2 (dlsup2), cause the complete transformation of the gynoecium into stamens. In these strong mutants, many ectopic stamens are formed in the region where the gynoecium is produced in the wild-type flower and they are arranged in a non-whorled, alternate pattern. The intermediate allele dl-1 (T65), results in an increase in the number of stamens and stigmas, and carpels occasionally show staminoid characteristics. In the weakest mutant, dl-2, most of the flowers are normal. All four dl alleles cause midrib-less drooping leaves. The flower of the double mutant, spw1 dl-sup, produces incompletely differentiated organs indefinitely after palea-like organs are produced in the position where lodicules are formed in the wild-type flower. These incompletely differentiated organs are neither stamens nor carpels, but have partial floral identity. Based on genetic and molecular results, we postulate a model of stamen and carpel specification in rice, with DL as a novel gene controlling carpel identity and acting mutually and antagonistically to the class B gene, SPW1.

The AGL6-like gene OsMADS6 regulates floral organ and meristem identities in rice

“…MADS-box proteins are able to form protein-protein complexes, which are required for their function [9,44,45]. In rice, the B class gene SPW1 (OsMADS16) [20] and the C class genes OsMADS3 and OsMADS58 [21], as well as the D class gene OsMADS13 play critical roles in specifying inner floral organ and meristem identities. OsMADS1/LHS1 has been shown to be a SEP-like gene that is required for determining identity of the lemma/ palea and the meristem of inner floral organs [25][26][27][28][29].…”

“…spw1 mutants display homeotic conversion of stamens to carpels and lodicules to palea/lemma-like structures [20]. Two class C genes OsMADS3 and OsMADS58 in rice have been shown to play distinct roles in specifying the identity of lodicules, stamens and carpels [21].…”

Time to Stop: Flower Meristem Termination

“…Thus, CRC, which specifically controls the female developmental program and is expressed from stage 6 on (Bowman and Smyth, 1999), also shares AG's function in FM termination, hence confirming the close link between these two processes. In the case of CRC, both functions seem to be widely conserved in angiosperms, as orthologs of CRC in various species display similar expression patterns in carpel primordia and loss-of-function phenotypes (Nagasawa et al, 2003;Yamaguchi et al, 2004;Fourquin et al, 2005;Lee et al, 2005;Orashakova et al, 2009). In rice, tobacco, petunia, and California poppy (Eschscholzia californica), this loss of function alone is sufficient to cause a strong loss of FM termination, suggesting that CRC orthologs play a more important role in this process in most species compared to Arabidopsis (Yamaguchi et al, 2004;Lee et al, 2005;Orashakova et al, 2009).…”

“…Conversely, mutants such as ag in Arabidopsis (Figs. 1, C and D, and 2B), plena (ple) in Antirrhinum (Antirrhinum majus), or drooping leaves in rice (Oryza sativa) exhibit a prolonged maintenance of stem cells within the FM, resulting in the production of extra organs borne on supernumerary whorls (Bowman et al, 1989(Bowman et al, , 1991Yanofsky et al, 1990;Bradley et al, 1993;Sieburth et al, 1995;Nagasawa et al, 2003). This phenotype, referred to as flower indeterminacy or loss of FM termination, is thus due to a temporal, rather than spatial, alteration of flower development.…”

The Maize PI/GLO Ortholog Zmm16/sterile tassel silky ear1 Interacts with the Zygomorphy and Sex Determination Pathways in Flower Development

“…The products of these MADS box genes regulate transcription by binding to specific DNA sequences known as CArG-boxes (Riechmann and Meyerowitz, 1997). Despite the unusual morphology of grass flowers, studies in both rice (Oryza sativa; Nagasawa et al, 2003;Yamaguchi et al, 2006;Dreni et al, 2011) and maize (Mena et al, 1996;Ambrose et al, 2000;Whipple et al, 2004) indicate that B and C functions are largely conserved between grasses and eudicot species, where these functions were originally defined. That C function is conserved across these species is perhaps not surprising, considering that their reproductive organs are clearly homologous.…”