Functional Characterization ofOsMADS18, a Member of theAP1/SQUASubfamily of MADS Box Genes  

Abstract

(G.F., M.M.A.) MADS box transcription factors controlling flower development have been isolated and studied in a wide variety of organisms. These studies have shown that homologous MADS box genes from different species often have similar functions. OsMADS18 from rice (Oryza sativa) belongs to the phylogenetically defined AP1/SQUA group. The MADS box genes of this group have functions in plant development, like controlling the transition from vegetative to reproductive growth, determination of floral organ identity, and regulation of fruit maturation. In this paper we report the functional analysis of OsMADS18. This rice MADS box gene is widely expressed in rice with its transcripts accumulated to higher levels in meristems. Overexpression of OsMADS18 in rice induced early flowering, and detailed histological analysis revealed that the formation of axillary shoot meristems was accelerated. Silencing of OsMADS18 using an RNA interference approach did not result in any visible phenotypic alteration, indicating that OsMADS18 is probably redundant with other MADS box transcription factors. Surprisingly, overexpression of OsMADS18 in Arabidopsis caused a phenotype closely resembling the ap1 mutant. We show that the ap1 phenotype is not caused by down-regulation of AP1 expression. Yeast two-hybrid experiments showed that some of the natural partners of AP1 interact with OsMADS18, suggesting that the OsMADS18 overexpression phenotype in Arabidopsis is likely to be due to the subtraction of AP1 partners from active transcription complexes. Thus, when compared to AP1, OsMADS18 during evolution seems to have conserved the mechanistic properties of protein-protein interactions, although it cannot complement the AP1 function.

The expression of two DEFICIENS-like genes was reduced in the sepaloid tepals of viridiflora tulips

“…In model plants of monocots, rice has four SQ-like genes, OsMADS14, OsMADS15, OsMADS18 and OsMADS20 (Fornara et al 2004). Among these genes, Preston and Kellogg (2007) discussed that OsMADS14 will concern identity of all floral organs and OsMADS15 have A-function because OsMADS14 is expressed in all floral organs except lodicules, and OsMADS15 is expressed only in the outer bracts and perianth (lodicules).…”

“…On the other hand, Jeon et al (2000) described over expression of OsMADS14 caused producing shoot, embryo and flower like structure from calli, but not mentioned change of floral organ identity. About OsMADS18, Fornara et al (2004) reported that it is widely expressed all plant tissues and cannot complement Afunction. In our opinion, it will be open question that OsMADS15 have A-function, because OsMADS15 lack the expression in rice lemma and palea, which are considered as rice sepal.…”

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

“…In addition, expression of three MADS box genes (out of 34 MADS box genes on the microarray) showed increases in expression between the V1 and the V/R stages ( Figures 2B and 2C). Intriguingly, these three genes are MADS14, MADS15, and MADS18, which belong to the AP1/FUL-like subfamily of MADS box genes (Litt and Irish 2003;Fornara et al, 2004;Preston and Kellogg, 2006; see Supplemental Figure 1 online). The only other member of this subfamily in rice, MADS20, showed no detectable expression in meristems at any of the stages examined in this study.…”

“…Despite a significant reduction in the levels of mRNA from each of these genes, neither inflorescence development nor flowering time was altered in single RNAi plants (see Supplemental Figure 4 online; Fornara et al, 2004). We then produced pMADS14;15;18i, an RNAi construct that simultaneously suppresses expression of MADS14, MADS15, and MADS18.…”

Genetic and Epigenetic Alteration among Three Homoeologous Genes of a Class E MADS Box Gene in Hexaploid Wheat

“…In wheat, it has been reported that the AP1-like gene WAP1 (sometimes called VRN1) (Murai et al, 1998) has no class A function but acts in phase transition from vegetative to reproductive growth (for diploid wheat, Yan et al, 2003; for hexaploid wheat, Danyluk et al, 2003;Murai et al, 2003;Trevaskis et al, 2003). Based on functional analysis using transgenic plants, the rice AP1-like genes Os MADS14 and Os MADS18 also play a role in the flowering pathway rather than specification of floral organs (Jeon et al, 2000;Fornara et al, 2004).…”