APETALA2 like genes from Picea abies show functional similarities to their Arabidopsis homologues

Abstract

In angiosperm flower development the identity of the floral organs is determined by the A, B and C factors. Here we present the characterisation of three homologues of the A class gene APETALA2 (AP2) from the conifer Picea abies (Norway spruce), Picea abies APETALA2 LIKE1 (PaAP2L1), PaAP2L2 and PaAP2L3. Similar to AP2 these genes contain sequence motifs complementary to miRNA172 that has been shown to regulate AP2 in Arabidopsis. The genes display distinct expression patterns during plant development; in the female-cone bud PaAP2L1 and PaAP2L3 are expressed in the seed-bearing ovuliferous scale in a pattern complementary to each other, and overlapping with the expression of the C class-related gene DAL2. To study the function of PaAP2L1 and PaAP2L2 the genes were expressed in Arabidopsis. The transgenic PaAP2L2 plants were stunted and flowered later than control plants. Flowers were indeterminate and produced an excess of floral organs most severely in the two inner whorls, associated with an ectopic expression of the meristem-regulating gene WUSCHEL. No homeotic changes in floral-organ identities occurred, but in the ap2-1 mutant background PaAP2L2 was able to promote petal identity, indicating that the spruce AP2 gene has the capacity to substitute for an A class gene in Arabidopsis. In spite of the long evolutionary distance between angiosperms and gymnosperms and the fact that gymnosperms lack structures homologous to sepals and petals our data supports a functional conservation of AP2 genes among the seed plants.

Expression patterns of LmAP2L1 and LmAP2L2 encoding two-APETALA2 domain proteins during somatic embryogenesis and germination of hybrid larch (Larix×marschlinsii).

“…This was also shown previously for the regulation of glossy15, which encoded a two-AP2 domain protein from maize (Lauter et al, 2005;Nilsson et al, 2007). L1 forms from Norway spruce, pine and hybrid larch showed that this site was totally complementary and located at the 3 0 end of cDNA.…”

“…Two explanations could be proposed: (i) the sequence of L2 form in pine is divergent due to a change in the selective pressure acting on the gene or (ii) the sequence corresponds to a paralogous gene and the real ortholog of L2 form in pine has not yet been identified. A third form was recently described in P. abies (Nilsson et al, 2007). PaAP2L3 is undoubtedly the sister group of Gnetum parvifolium AP2, with a bootstrap proportion of 98%.…”

“…APETALA2-like genes were also characterized in Norway spruce (Picea abies (L.) Karst) and pine (Pinus thunbergii Parl.) (Vahala et al, 2001;Shigyo and Ito, 2004;Nilsson et al, 2007). We hypothesized that these proteins could also be characterized in hybrid larch, where they may play a role in somatic embryogenesis.…”

A putative miR172-targeted CeAPETALA2-like gene is involved in floral patterning regulation of the orchid Cymbidium ensifolium

“…Relatively high degrees of homology were also indicated between this cDNA and the AP2-like sequences from Arabidopsis. Additionally, we showed strong complementarity between CeAP2-like mRNA and miR172, as well as localization of the complementary nucleotides similar to that in the cDNAs of other homologous genes identified in different plant species (Nilsson et al, 2007;Varkonyi-Gasic et al, 2012). These results indicated the potential regulation of AP2 by miR172 in the orchid.…”

Identification of conserved microRNAs and their target genes in tomato (Lycopersicon esculentum)

“…In fact, miR156 and miR172 are expressed in opposite temporal patterns, suggesting that the miR156 module may regulate the expression of miR172 (Willmann and Poethig, 2007). In addition, Nilsson et al (2007) suggested that the AP2 gene in spruce has the capacity to substitute an A class gene required in flower development. Additional studies are now required to determine the basis for this regulation and the complicated regulating network.…”