With approximately 352,000 living species on Earth, the flowering plants or angiosperms constitute the largest and most diverse extant group of the plant kingdom, and about 90% of land plant species. The rapid appearance and diversification of angiosperms which is documented by fossils have been defined as ‘abominable mystery’ by Charles Darwin. Certainly, the evolution of new reproductive structures like the flower and its female part, the pistil, had a major role in the extraordinary evolutive success of angiosperms. How these structures evolved, also at molecular level, is however still unknown. In addition, after pollination the pistil and the ovule(s) within develop into fruit and seed(s) respectively, which are the edible part of most crops. Therefore, molecular studies on pistil development can both help clarify one of the bigger ‘secrets’ of plant evolution, and bring significant advantages and tools for targeted crop improvement. Despite information about genetic control of pistil identity and patterning is already available, these data mainly pertain to Arabidopsis and few other eudicot model plants. Therefore, these genetic mechanisms could either explain the evolution of the pistil in the earliest ancestors of all flowering plants, or represent more recent novelties reflecting the adaptation of eudicots. Therefore, comparative studies are needed in the other largest and most evolved group of flowering plants, the monocots, and also in basal angiosperms. This Marie Curie action ‘Ricestyle’ aims to clarify part of the ‘abominable mystery’ by the comparative study of pistil development and its genetic basis in rice, which is by far the main monocot model plant and, together the other cereals, the main source of calories for human diet.
During the first phase of the project, in the Host Laboratory of Prof. Dabing Zhang (Shanghai Jiao Tong University, China) we have developedall the tools necessary for the functional characterization of the candidate genes which might be involved in pistil tissue identity and patterning. Based on the homology with genes known in Arabidopsis thaliana and other eudicot model plants, we have search in the rice genome for phylogenetically related and functionally equivalent genes. Our work has yielded a complete study of the evolutionary history of these gene families that will be the base for our functional studies.
In addition, the collaboration between the two Host Labs allowed the characterization of three other transcription factors belonging to the SEPALLATA MADS-box subfamily. These factors confer the identity of all the floral organs including the pistil, thus they are master regulators acting upstream also of the moleculart network for carpel development. The work has been published recently on Plant Physiology (Wu D, Liang W, Zhu W, Chen M, Ferrandiz C, Burton RA, Dreni L, Zhang D. Plant Physiol. 2017 Dec 7. pii: pp.00704.2017. doi: 10.1104/pp.17.00704).
Moreover, we have isolated a gene encoding for a glutaredoxin which is important for the pistil development in rice. Loss of function mutants cannot produce pistils in about half of the spikelet, otherwise produce reduced pistils. These results are somehow unexpected and may represent a monocot evolutionary innovation or, otherwise, be also important in dicots, only unexplored so far. Thus,they may provide a two-way pathway to improve our knowledge in pistil morphogenesis in angiosperms. A first paper describing the function of this glutaredoxin and its genetic interaction with floral and carpel identity genes will be submitted soon.
In the second phase of the project we have continued the phenotyping and the characterization of the above mentioned mutants, and also created higher order mutants. The data from these experiments indicated a number of genes with essential function in determining the correct carpel morphology in rice. We are deeply characterizing the molecular networks regulated by these genes and we aim to publish our findings soon.
