A multidisciplinary approach to gain sustainable improvement of rice productivity through the co-cultivation with the fern Azolla and its cyanobacterial symbiont

Achieving a steady increase in cereal crop yield has become a top research priority. The increment of world population, expected to reach 10 billion by 2050, coupled to food shortage, poses in fact a serious threat to social and political stability. Globally, food crop yields are already dangerously stagnating, indicating that further yield gains through conventional breeding and increased use of soil fertilizers are strategies that are not more pursuable. Further to this, enhanced plant productivity has to be achieved while preventing extensive land-use increase, deforestation, biodiversity loss, and environmental pollution. Therefore, urgent alternative and sustainable strategies to keep yield improvement in pace with world-wide population growth is mandatory. This multidisciplinary research proposal focuses on sustainable yield increase in rice grain production through the co-cultivation with Azolla-Anabaena. Rice (Oryza sativa) is both a model grass species and the world’s second-most produced staple cereal crop. Azolla is an aquatic pteridophyte that has co-evolved with Anabaena azollae, a symbiotic nitrogen fixing cyanobacteria inhabiting the fern leaflets. In Asia Azolla co-cultivation with rice has been used for many centuries as an organic nitrogen fertilizer in wetland rice cultivation whereas in Europe its use is limited. The benefits of Azolla as a bio-fertilizer are well documented through decades of agronomic studies aimed at improving nitrogen use efficiency in rice. Beyond that, in virtue of their capacity to emit volatile organic compounds (BVOCs) and other signalling molecules (i.e hormones), the Azolla-Anabaena symbionts might positively interfere with rice plant development and resilience, thereby representing a potential natural resource to grow rice sustainably. Unfortunately, the nature of molecular interactions and the effects of the BVOCs emitted from Azolla-Anabaena on rice plants still remain unknown and unexplored. This project uses a multidisciplinary approach involving, physiological, molecular and genetic research to investigate the role of BVOCs emitted from Azolla-Anabaena in rice plant development, grain productivity and tolerance to environmental stresses. In particular, this project will first investigate in vivo the emission of BVOCs by Azolla-Anabaena both qualitatively and quantitatively. Then, the effects of the co-cultivation with Azolla-Anabaena on rice plant development (roots, shoots and inflorescences) will be investigated in detail by high-throughput phenotyping. Traits related to rice growth, productivity but also tolerance to abiotic stresses will be thoroughly addressed. To gain insight on how exogenous BVOCs exert beneficial effects on rice, the rice regulatory network controlling responses to BVOCs will be studied. Regulatory genes will be identified by transcriptome analysis using a next generation sequencing approach. Mutants for candidate genes will be obtained through a CRISPR-Cas9 genome editing approach or by overexpression analysis and functionally characterized upon application of specific exogenous BVOCs or co-cultivation with Azolla-Anabaena. The know-how generated in this project will create important opportunities for (molecular) breeding programmes focused on rice germplasm that will fully exploit the beneficial effects of Azolla-Anabaena co-cultivation. In turn, this project will provide fundamental evidence on the interplay between crop plants and BVOCs emitted by other organisms being of pivotal importance for breeding and management of other crops. Importantly, this project is a beautiful showcase to demonstrate the valuable solutions for sustainable agriculture. On this concern, the achieved results will be disseminated to breeders, farmers and consumers.