Unique and redundant functional domains of APETALA1 and CAULIFLOWER, two recently duplicated Arabidopsis thaliana floral MADS-box genes

Abstract

APETALA1 (AP1) and CAULIFLOWER (CAL) are closely related MADS box genes that are partially redundant during Arabidopsis thaliana floral meristem determination. AP1 is able to fully substitute for CAL functions, but not vice versa, and AP1 has unique sepal and petal identity specification functions. In this study, the unique and redundant functions of these two genes has been mapped to the four protein domains that characterize type-II MADS-domain proteins by expressing all 15 chimeric combinations of AP1 and CAL cDNA regions under control of the AP1 promoter in ap1-1 loss-of-function plants. The "in vivo" function of these chimeric genes was analysed in Arabidopsis plants by expressing the chimeras. Rescue of flower meristem and sepal/petal identities was scored in single and multiple insert homozygous transgenic lines. Using these chimeric lines, it was found that distinct residues of the AP1 K domain not shared by the same CAL domain are necessary and sufficient for complete recovery of floral meristem identity, in the context of the CAL protein sequence, while both AP1 COOH and K domains are indispensable for complete rescue of sepal identity. By contrast, either one of these two AP1 domains is necessary and sufficient for complete petal identity recovery. It was also found that there were positive and negative synergies among protein domains and their combinations, and that multiple-insert lines showed relatively better rescue than equivalent single-insert lines. Finally, several lines had flowers with extra sepals and petals suggesting that chimeric proteins yield abnormal transcriptional complexes that may alter the expression or regulation of genes that control floral organ number under normal conditions.

Evolution of fruit development genes in flowering plants

“…The duplication itself has low BS, but the euFULI and euFULII clades have high support with 81 and 74, respectively. Within Brassicaceae another duplication occurred within the euAP1 clade resulting in the AP1 and CAL Brassicaceae gene clades (100 BS) (Figure 3; Lowman and Purugganan, 1999; Alvarez-Buylla et al, 2006). Major sequence changes are linked with the core-eudicot duplication.…”

“…Major sequence changes are linked with the core-eudicot duplication. Whereas euFUL proteins retain the characteristic FUL-like motif present in FUL-like pre-duplication proteins present in basal angiosperms, monocots and basal eudicots, the euAP1 proteins acquired, due to a frameshift mutation, a transcription activation and a farnesylation motif at the C-terminus (Cho et al, 1999; Yalovsky et al, 2000; Litt and Irish, 2003; Preston and Kellogg, 2006; Shan et al, 2007), that is very conserved in CAL proteins as well Kempin et al (1995); Alvarez-Buylla et al (2006). …”

Gain of An Auto-regulatory Site Led to Divergence of the Arabidopsis APETALA1 and CAULIFLOWER Duplicate Genes in the Time, Space and Level of Expression and Regulation of One Paralog by the Other

“…Up to now, it has been shown that (1) the protein products of the two genes, AP1 and CAL, have redundant but slightly differentiated functions, being able to interact with different numbers and sets of partners (Riechmann et al, 1996a(Riechmann et al, , 1996bPelaz et al, 2001;de Folter et al, 2005;Kaufmann et al, 2005;Smaczniak et al, 2012); (2) the amino acid differences in the K and C regions of the AP1 and CAL proteins are responsible for their differences in function, whereas the M and I regions, which play key roles in binding to CREs of downstream genes, are functionally indistinguishable (Alvarez-Buylla et al, 2006); and (3) the expression of the AP1 and CAL genes is precisely controlled by many regulators, of which the vast majority are transcription factors (i.e. trans-regulatory elements; Wagner et al, 1999;Wigge et al, 2005;Saddic et al, 2006;Sundström et al, 2006;Kaufmann et al, 2009;Mathieu et al, 2009;Wang et al, 2009;Yamaguchi et al, 2009;Xu et al, 2010;Yant et al, 2010;Pastore et al, 2011).…”

PoppyAPETALA1/FRUITFULLOrthologs Control Flowering Time, Branching, Perianth Identity, and Fruit Development

“…Within the Brassicaceae, an additional duplication occurred in the euAP1 gene clade, producing the Arabidopsis paralogs CAULIFLOWER (CAL) and AP1 (Lowman and Purugganan, 1999;Alvarez-Buylla et al, 2006). AP1 and CAL are expressed in floral meristems and in developing sepal and petal primordia (Mandel et al, 1992;Kempin et al, 1995;Ferrándiz et al, 2000;Blázquez et al, 2006); expression patterns of orthologs in other core eudicots are for the most part similar, although they may also include bracts and reproductive organs (Huijser et al, 1992;Hardenack et al, 1994;Berbel et al, 2001;Shchennikova et al, 2004;Sather and Golenberg, 2009).…”