Several MADS box gene lineages involved in flower development have undergone duplications that correlate with the diversification of large groups of flowering plants. In the APETALA1 gene lineage, a major duplication coincides with the origin of the core eudicots, resulting in the euFUL and the euAP1 clades. Arabidopsis FRUITFULL (FUL) and APETALA1 (AP1) function redundantly in specifying floral meristem identity but function independently in sepal and petal identity (AP1) and in proper fruit development and determinacy (FUL). Many of these functions are largely conserved in other core eudicot euAP1 and euFUL genes, but notably, the role of APETALA1 as an "A-function" (sepal and petal identity) gene is thought to be Brassicaceae specific. Understanding how functional divergence of the core eudicot duplicates occurred requires a careful examination of the function of preduplication (FUL-like) genes. Using virus-induced gene silencing, we show that FUL-like genes in opium poppy (Papaver somniferum) and California poppy (Eschscholzia californica) function in axillary meristem growth and in floral meristem and sepal identity and that they also play a key role in fruit development. Interestingly, in opium poppy, these genes also control flowering time and petal identity, suggesting that AP1/FUL homologs might have been independently recruited in petal identity. Because the FUL-like gene functional repertoire encompasses all roles previously described for the core eudicot euAP1 and euFUL genes, we postulate subfunctionalization as the functional outcome after the major AP1/FUL gene lineage duplication event.

The genetic mechanisms regulating dry fruit development and opercular dehiscence have been identified in Arabidopsis thaliana. In the bicarpellate silique, valve elongation and differentiation is controlled by FRUITFULL (FUL) that antagonizes SHATTERPROOF1-2 (SHP1/SHP2) and INDEHISCENT (IND) at the dehiscence zone where they control normal lignification. SHP1/2 are also repressed by REPLUMLESS (RPL), responsible for replum formation. Similarly, FUL indirectly controls two other factors ALCATRAZ (ALC) and SPATULA (SPT) that function in the proper formation of the separation layer. FUL and SHP1/2 belong to the MADS-box family, IND and ALC belong to the bHLH family and RPL belongs to the homeodomain family, all of which are large transcription factor families. These families have undergone numerous duplications and losses in plants, likely accompanied by functional changes. Functional analyses of homologous genes suggest that this network is fairly conserved in Brassicaceae and less conserved in other core eudicots. Only the MADS box genes have been functionally characterized in basal eudicots and suggest partial conservation of the functions recorded for Brassicaceae. Here we do a comprehensive search of SHP, IND, ALC, SPT, and RPL homologs across core-eudicots, basal eudicots, monocots and basal angiosperms. Based on gene-tree analyses we hypothesize what parts of the network for fruit development in Brassicaceae, in particular regarding direct and indirect targets of FUL, might be conserved across angiosperms.

SUMMARYThe APETALA1/FRUITFULL (AP1/FUL) MADS box transcription factors are best known for the role of AP1 in Arabidopsis sepal and petal identity, the canonical A function of the ABC model of flower development. However, this gene lineage underwent multiple duplication events during angiosperm evolution, providing different taxa with unique gene complements. One such duplication correlates with the origin of the core eudicots, and produced the euAP1 and euFUL clades. Together, euAP1 and euFUL genes function in proper floral meristem identity and repression of axillary meristem growth. Independently, euAP1 genes function in floral meristem and sepal identity, whereas euFUL genes control phase transition, cauline leaf growth and fruit development. To investigate the impact of the core eudicot duplication on the functional diversification of this gene lineage, we studied the role of pre-duplication FUL-like genes in columbine (Aquilegia coerulea). Our results show that AqcFL1 genes are broadly expressed in vegetative and reproductive meristems, leaves and flowers. Virus-induced gene silencing of the loci results in plants with increased branching, shorter inflorescences with fewer flowers, and dramatic changes in leaf shape and complexity. However, aqcfl1 plants have normal flowers and fruits. Our results show that, in contrast to characterized AP1/FUL genes, the AqcFL1 loci are either genetically redundant or have been decoupled from the floral genetic program, and play a major role in leaf morphogenesis. We analyze the results in the context of the core eudicot duplication, and discuss the implications of our findings in terms of the genetic regulation of leaf morphogenesis in Aquilegia and other flowering plants.

SUMMARYFlower monosymmetry contributes to specialized interactions between plants and their insect pollinators. In the magnoliids, flower monosymmetry is exhibited only in the Aristolochiaceae (Piperales). Aristolochia flowers develop a calyx-derived monosymmetric perianth that enhances pollination success by a flytrap mechanism. Aristolochia arborea forms additionally a special perianth outgrowth that mimics a mushroom to attract flies, the mushroom mimicry structure (MMS). In core eudicots, members of the CYC2 clade of TCP transcription factors are key regulators of corolla monosymmetry establishment. The CYC2 clade arose via core eudicot-specific duplications from ancestral CYC/TB1 genes. CYC/TB1 genes are also thought to affect monosymmetry formation in early diverging eudicot and monocot species. Here, we demonstrate that CYC/TB1 genes, named CYC-like genes (CYCL) are present in basal angiosperms and magnoliids. Expression analyses in A. arborea indicate that CYCL genes participate in perianth and MMS differentiation processes and do not support a CYCL gene function in initial flower monosymmetry formation. Heterologous CYCL and CYC2 gene overexpression studies in Arabidopsis show that Aristolochia CYCL proteins only perform a CYC2-like function when the CYCL TCP domain is replaced by a CYC2 domain. Comparative TCP domain analyses revealed that an LxxLL motif, known to mediate protein-protein interactions, evolved in the second helix of the TCP domain in the CYC2 lineage and contributes to CYC2-related functions. Our data imply that divergent evolution of the CYC/TB1 lineages caused significant changes in their coding regions, which together with cis-regulatory changes established the key CYC2 function in regulating eudicot flower monosymmetry.

Ontogenetically, all fleshy or all dry fruits do not necessarily share a common developmental ground plan. Independent evolution of fleshiness, sclerification, dryness, and dehiscence are discussed in a phylogenetic context.

Aristolochia fimbriata (Aristolochiaceae: Piperales) exhibits highly synorganized flowers with a single convoluted structure forming a petaloid perianth that surrounds the gynostemium, putatively formed by the congenital fusion between stamens and the upper portion of the carpels. Here we present the flower development and morphology of A. fimbriata, together with the expression of the key regulatory genes that participate in flower development, particularly those likely controlling perianth identity. A. fimbriata is a member of the magnoliids, and thus gene expression detected for all ABCE MADS-box genes in this taxon, can also help to elucidate patterns of gene expression prior the independent duplications of these genes in eudicots and monocots. Using both floral development and anatomy in combination with the isolation of MADS-box gene homologs, gene phylogenetic analyses and expression studies (both by reverse transcription PCR and in situ hybridization), we present hypotheses on floral organ identity genes involved in the formation of this bizarre flower. We found that most MADS-box genes were expressed in vegetative and reproductive tissues with the exception of AfimSEP2, AfimAGL6, and AfimSTK transcripts that are only found in flowers and capsules but are not detected in leaves. Two genes show ubiquitous expression; AfimFUL that is found in all floral organs at all developmental stages as well as in leaves and capsules, and AfimAG that has low expression in leaves and is found in all floral organs at all stages with a considerable reduction of expression in the limb of anthetic flowers. Our results indicate that expression of AfimFUL is indicative of pleiotropic roles and not of a perianth identity specific function. On the other hand, expression of B-class genes, AfimAP3 and AfimPI, suggests their conserved role in stamen identity and corroborates that the perianth is sepal and not petal-derived. Our data also postulates an AGL6 ortholog as a candidate gene for sepal identity in the Aristolochiaceae and provides testable hypothesis for a modified ABCE model in synorganized magnoliid flowers.

The gynoecium patterning and fruit developmental genetic network in the Brassicaceae cannot be directly extrapolated to the Solanaceae. In Solanaceae ALC, SPT and RPL contribute differently to maturation of dry dehiscent and fleshy fruits, whereas HEC genes are not generally expressed in the gynoecium. RPL genes have broader expression patterns than expected.

In parasitic plants, the reduction in plastid genome (plastome) size and content is driven predominantly by the loss of photosynthetic genes. The first completed mitochondrial genomes (mitogenomes) from parasitic mistletoes also exhibit significant degradation, but the generality of this observation for other parasitic plants is unclear. We sequenced the complete mitogenome and plastome of the hemiparasite Castilleja paramensis (Orobanchaceae) and compared them with additional holoparasitic, hemiparasitic and nonparasitic species from Orobanchaceae. Comparative mitogenomic analysis revealed minimal gene loss among the seven Orobanchaceae species, indicating the retention of typical mitochondrial function among Orobanchaceae species. Phylogenetic analysis demonstrated that the mobile cox1 intron was acquired vertically from a nonparasitic ancestor, arguing against a role for Orobanchaceae parasites in the horizontal acquisition or distribution of this intron. The C. paramensis plastome has retained nearly all genes except for the recent pseudogenization of four subunits of the NAD(P)H dehydrogenase complex, indicating a very early stage of plastome degradation. These results lend support to the notion that loss of ndh gene function is the first step of plastome degradation in the transition to a parasitic lifestyle.