The Role of Cytokinins during the Development of Strawberry Flowers and Receptacles.

Cytokinins play a relevant role in flower and fruit development and plant yield. Strawberry fruits have a high commercial value, although what is known as the "fruit" is not a "true" botanical fruit because it develops from a non-reproductive organ (receptacle) on which the true botanical fruits (achenes) are found. Given cytokinins' roles in botanical fruits, it is important to understand their participation in the development of a non-botanical or accessory "fruit". Therefore, in this work, the role of cytokinin in strawberry flowers and fruits was investigated by identifying and exploring the expression of homologous genes for different families that participate in the pathway, through publicly available genomic and expression data analyses. Next, trans-zeatin content in developing flowers and receptacles was determined. A high concentration was observed in flower buds and at anthesis and decreased as the fruit approached maturity. Moreover, the spatio-temporal expression pattern of selected CKX genes was evaluated and detected in receptacles at pre-anthesis stages. The results point to an important role and effect of cytokinins in flower and receptacle development, which is valuable both from a biological point of view and to improve yield and the quality of this fruit.

Expression of gynoecium patterning transcription factors in Aristolochia fimbriata (Aristolochiaceae) and their contribution to gynostemium development.

BACKGROUND: In Aristolochia (Aristolochiaceae) flowers, the congenital fusion of the anthers and the commissural, stigmatic lobes forms a gynostemium. Although the molecular bases associated to the apical-basal gynoecium patterning have been described in eudicots, comparative expression studies of the style and stigma regulatory genes have never been performed in early divergent angiosperms possessing a gynostemium. RESULTS: In this study, we assess the expression of five genes typically involved in gynoecium development in Aristolochia fimbriata. We found that all five genes (AfimCRC, AfimSPT, AfimNGA, AfimHEC1 and AfimHEC3) are expressed in the ovary, the placenta, the ovules and the transmitting tract. In addition, only AfimHEC3, AfimNGA and AfimSPT are temporarily expressed during the initiation of the stigma, while none of the genes studied is maintained during the elaboration of the stigmatic surfaces in the gynostemium. CONCLUSIONS: Expression patterns suggest that CRC, HEC, NGA and SPT homologs establish ovary and style identity in Aristolochia fimbriata. Only NGA,HEC3 and SPT genes may play a role in the early differentiation of the stigmatic lobes, but none of the genes studied seems to control late stigma differentiation in the gynostemium. The data gathered so far raises the possibility that such transient expression early on provides sufficient signal for late stigma differentiation or that unidentified late identity genes are controlling stigma development in the gynostemium. Our data does not rule out the possibility that stigmas could correspond to staminal filaments with convergent pollen-receptive surfaces.

Expression and function of the bHLH genes ALCATRAZ and SPATULA in selected Solanaceae species.

The genetic mechanisms underlying fruit development have been identified in Arabidopsis and have been comparatively studied in tomato as a representative of fleshy fruits. However, comparative expression and functional analyses on the bHLH genes downstream the genetic network, ALCATRAZ (ALC) and SPATULA (SPT), which are involved in the formation of the dehiscence zone in Arabidopsis, have not been functionally studied in the Solanaceae. Here, we perform detailed expression and functional studies of ALC/SPT homologs in Nicotiana obtusifolia with capsules, and in Capsicum annuum and Solanum lycopersicum with berries. In Solanaceae, ALC and SPT genes are expressed in leaves, and all floral organs, especially in petal margins, stamens and carpels; however, their expression changes during fruit maturation according to the fruit type. Functional analyses show that downregulation of ALC/SPT genes does not have an effect on gynoecium patterning; however, they have acquired opposite roles in petal expansion and have been co-opted in leaf pigmentation in Solanaceae. In addition, ALC/SPT genes repress lignification in time and space during fruit development in Solanaceae. Altogether, some roles of ALC and SPT genes are different between Brassicaceae and Solanaceae; while the paralogs have undergone some subfunctionalization in the former they are mostly redundant in the latter.

Evolution of genes associated with gynoecium patterning and fruit development in Solanaceae.

Background and Aims: The genetic basis of fruit development has been extensively studied in Arabidopsis, where major transcription factors controlling valve identity (i.e. FRUITFULL), replum development (i.e. REPLUMLESS) and the differentiation of the dehiscence zones (i.e. SHATTERPROOF, INDEHISCENT and ALCATRAZ) have been identified. This gene regulatory network in other flowering plants is influenced by duplication events during angiosperm diversification. Here we aim to characterize candidate fruit development genes in the Solanaceae and compare them with those of Brassicaceae. Methods: ALC/SPT, HEC/IND, RPL and AG/SHP homologues were isolated from publicly available databases and from our own transcriptomes of Brunfelsia australis and Streptosolen jamesonii. Maximum likelihood phylogenetic analyses were performed for each of the gene lineages. Shifts in protein motifs, as well as expression patterns of all identified homologues, are shown in dissected floral organs and fruits in different developmental stages of four Solanaceae species exhibiting different fruit types. Key Results: Each gene lineage has undergone different duplication time-points, resulting in very different genetic complements in the Solanaceae when compared with the Brassicaceae. In general, Solanaceae species have more copies of HEC1/2 and RPL than Brassicaceae, have fewer copies of SHP and the same number of copies of AG, ALC and SPT. Solanaceae lack IND orthologues, but have pre-duplication HEC3 homologues. The expression analyses showed opposite expression of SPT and ALC orthologues between dry- and fleshy-fruited species during fruit maturation. Fleshy-fruited species turn off RPL and SPT orthologues during maturation. Conclusions: 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.