Inflorescence Meristem Identity in Rice Is Specified by Overlapping Functions of Three AP1/FUL-Like MADS Box Genes and PAP2, a SEPALLATA MADS Box Gene

Abstract

In plants, the transition to reproductive growth is of particular importance for successful seed production. Transformation of the shoot apical meristem (SAM) to the inflorescence meristem (IM) is the crucial first step in this transition. Using laser microdissection and microarrays, we found that expression of PANICLE PHYTOMER2 (PAP2) and three APETALA1 (AP1)/ FRUITFULL (FUL)-like genes (MADS14, MADS15, and MADS18) is induced in the SAM during meristem phase transition in rice (Oryza sativa). PAP2 is a MADS box gene belonging to a grass-specific subclade of the SEPALLATA subfamily. Suppression of these three AP1/FUL-like genes by RNA interference caused a slight delay in reproductive transition. Further depletion of PAP2 function from these triple knockdown plants inhibited the transition of the meristem to the IM. In the quadruple knockdown lines, the meristem continued to generate leaves, rather than becoming an IM. Consequently, multiple shoots were formed instead of an inflorescence. PAP2 physically interacts with MAD14 and MADS15 in vivo. Furthermore, the precocious flowering phenotype caused by the overexpression of Hd3a, a rice florigen gene, was weakened in pap2-1 mutants. Based on these results, we propose that PAP2 and the three AP1/FUL-like genes coordinately act in the meristem to specify the identity of the IM downstream of the florigen signal.

RiceLHS1/OsMADS1Controls Floret Meristem Specification by Coordinated Regulation of Transcription Factors and Hormone Signaling Pathways

“…OsMADS34 transcripts are at reduced levels in the young FM. In contrast, OsMADS1 transcripts are abundant in the incipient FM and nearly undetectable in empty glumes (Prasad et al, 2001;Gao et al, 2010;Kobayashi et al, 2010Kobayashi et al, , 2012. We found 4-fold increased transcript levels for OsMADS34 in PUbi: OsMADS1-DGR; P35S:OsMADS1amiR panicles (Fig.…”

“…But members of a grassspecific subgroup in the LOFSEP clade, OsMADS1, OsMADS5, and OsMADS34, have acquired novel functions (Malcomber and Kellogg, 2005;Gao et al, 2010;Kobayashi et al, 2010). OsMADS34 regulates panicle branching and promotes spikelet meristem and empty glume fate (Gao et al, 2010;Kobayashi et al, 2010Kobayashi et al, , 2012. OsMADS1 is expressed developmentally slightly later and is restricted to the incipient FM region of the spikelet and controls its fate (Jeon et al, 2000;Prasad et al, 2005).…”

“…OsMADS34, a rice LOFSEP member, regulates inflorescence branching and promotes spikelet meristem fate (Gao et al, 2010;Kobayashi et al, 2010Kobayashi et al, , 2012 and thus is suggested to act temporally earlier than OsMADS1. In developing panicles, spikelets, and florets, these two genes have partly exclusive and some overlapping expression patterns (Kobayashi et al, 2010).…”

Direct links between the vernalization response and other key traits of cereal crops

“…Other genes that show altered expression during early development but are not bound by the VRN1 protein might be indirectly regulated by increased activity of the VRN1 gene. For example, the expression of Barley MADS3, an APETALA-like (AP1) MADS box gene, is possibly activated by increased FT1 activity, since FT-like genes are known to activate the expression of AP1-like MADS box genes that play critical roles during later stages inflorescence development in cereal 44,45 .…”

Regulatory modules controlling maize inflorescence architecture

“…Although these programs are largely conserved across eudicots, we know little about how such mechanisms extend to grasses and/or to what extent novel factors have been recruited to pattern grass-specific inflorescence morphology. Some clues have emerged from expression profiling studies of grass inflorescence development, for example, in rice (Oryza sativa) (Furutani et al 2006;Kobayashi et al 2012). However, while homologs exist in other species, ra1 and ra3 themselves are found only within a clade known as the Panicoid grasses (Vollbrecht et al 2005;Doust 2007;Kellogg 2007), and it has been suggested that they function in a regulatory module that either was lost in other grass lineages or arose in Panicoids via subfunctionalization.…”