Transcriptome landscape of Rafflesia cantleyi floral buds reveals insights into the roles of transcription factors and phytohormones in flower development.

Rafflesia possesses unique biological features and known primarily for producing the world's largest and existing as a single flower. However, to date, little is known about key regulators participating in Rafflesia flower development. In order to further understand the molecular mechanism that regulates Rafflesia cantleyi flower development, RNA-seq data from three developmental stages of floral bud, representing the floral organ primordia initiation, floral organ differentiation, and floral bud outgrowth, were analysed. A total of 89,890 transcripts were assembled of which up to 35% could be annotated based on homology search. Advanced transcriptome analysis using K-mean clustering on the differentially expressed genes (DEGs) was able to identify 12 expression clusters that reflect major trends and key transitional states, which correlate to specific developmental stages. Through this, comparative gene expression analysis of different floral bud stages identified various transcription factors related to flower development. The members of WRKY, NAC, bHLH, and MYB families are the most represented among the DEGs, suggesting their important function in flower development. Furthermore, pathway enrichment analysis also revealed DEGs that are involved in various phytohormone signal transduction events such as auxin and auxin transport, cytokinin and gibberellin biosynthesis. Results of this study imply that transcription factors and phytohormone signalling pathways play major role in Rafflesia floral bud development. This study provides an invaluable resource for molecular studies of the flower development process in Rafflesia and other plant species.

Expression pattern of CUC3 ortholog in Zeylanidium tailichenoides (Podostemaceae) infers organization of a unique distichous shoot in Podostemoideae.

Shoots of the aquatic eudicot family, Podostemaceae, exhibit unusual organogenesis with mixed leaf and stem identities. New shoots arise at the base of the older shoot with shoot apical meristem (SAM) identity but the entire SAM differentiates into a "leaf" as it develops in the Podostemoideae subfamily. The "leaves" are tightly arranged in a zigzag manner to form an apparent distichous shoot as a whole. Although previous studies have suggested that Podostemoideae shoots have evolved by modifying the ancestral sympodial branching system in the basal Tristichoideae subfamily, this evolutionary scenario requires elucidation at the molecular level. To confirm that the shoots arise as axillary shoots, in the present study, we examined gene expression patterns in plumular shoots of Zeylanidium tailichenoides using CUP-SHAPED COTYLEDON 3 (CUC3) and SHOOT MERISTEMLESS (STM) orthologs, which are involved in the determination of axils and meristem formation in model plants. Expression of the CUC3 ortholog was detected at the adaxial base of cotyledons and parental shoots where the new shoots are initiated, while STM ortholog was expressed at the initiation site and in the young shoot primordia throughout early shoot development. The results demonstrate that each Z. tailichenoides shoot arises as an axillary bud in a manner similar to axillary meristem formation in model plants involving CUC3 and STM genes. Considering that each of the two cotyledons produces an axillary bud that in turn continues to form its own axillary bud independently, the apparent distichous shoot in Z.tailichenoides is not a single shoot, but a composite of two sympodially branched shoots.

Structure and development of flowers and inflorescences in Peraceae and Euphorbiaceae and the evolution of pseudanthia in Malpighiales.

Pseudanthia are reduced and compact inflorescences which apparently had independent evolution in Euphorbiaceae and Peraceae within Malpighiales. In order to analyze the hypothesis that the different pseudanthia found in Malpighiales have non-homologous developmental steps, we studied the inflorescence and flower development in the three Malpighiales genera that present this type of inflorescence-Dalechampia (Acalyphoideae/Euphorbiaceae), Euphorbia (Euphorbioideae/Euphorbiaceae), and Pera (Peraceae)-and compared them to that of Joannesia (Crotonoideae/Euphorbiaceae), which does not present a pseudanthium. Inflorescences and flowers were analyzed using light microscopy and scanning electron microscopy. Dalechampia and Euphorbia have protogynic bisexual pseudanthia, with unisexual perianthed flowers in Dalechampia, and achlamydeous flowers in Euphorbia. Pera has unisexual pseudanthia and the male flowers have a vestigial calyx and the female flowers are achlamydeous. Joannesia flowers are very distinct when compared to the pseudanthia flowers, as they are composed of all the whorls and there is no reduction. In the early stages of development, the first structures to be formed in the pseudanthia are the different series of bracts, including outer, involucral and involucel bracts. The floral primordia are initiated almost simultaneously with the involucre. Although the different morphology, the early inflorescence followed the same branching pattern in all studied genera, and the number and elongation of the branches were affected by the early female flower development in the terminal position. We suggest that the different pseudanthia evolved via process of floral whorl reduction and reorganization of flowers in the inflorescence axes, especially the position of female and male flowers and elongation or shortening of the branches. The sex of the terminal flower is a developmental key, i.e., the protogynic development deeply affects the pseudanthia growth, reducing the ramification and elongation of the axes.

Lebbiea (Podostemaceae-Podostemoideae), a new, nearly extinct genus with foliose tepals, in Sierra Leone.

Lebbiea grandiflora (Podostemaceae), a rheophytic herb from the Sewa River rapids in Sierra Leone, is described as a new species. It is the first new African genus of Podostemaceae published for 30 years. First collected in May 2017, the species is assessed as Critically Endangered using the IUCN 2012 standard. It is on the edge of extinction with a small population at a single site threatened by deposition of gravel and sand from alluvial gold and diamond mining upstream, and a planned hydro-electric dam. The new genus is unique in Podostemaceae in a) its highly developed and robust style-stigma structure in which the bases of the two style-stigmas unite to form a bifurcate funneliform-cylindrical structure, with a reflexed, blade-like apex that extends half-way around the perimeter of the ovary-fruit towards the base of the ovary-fruit, b) a specialised andropodium, with robust, self-supporting capacity, having differentiated thickened central, and angled, thinner marginal areas (in other Podostemaceae the andropodial structures are undifferentiated), c) the pillar-like haptera which completely elevate the crustose root above the substrate. Lebbiea is placed in Podostemoideae, necessitating amplification of the delimitation of that subfamily in which it is additionally unique in having the foliose tepals characteristic of the basal subfamilies Weddellinoideae and Tristichoideae.