Azolla mediated alterations in grain yield and quality in Rice

Rice is one of the most important cereal crops worldwide. To boost its production in a sustainable manner, co-cultivation with Azolla species is often used to supplement its nitrogen (N) demands. However, beyond N nutrition, the physiological and developmental effects of azolla on rice remain unclear. This study investigates these mechanisms by analysing growth, inflorescence meristem transcriptomics, yield, and grain ionomics in rice plants grown alone (R) or with azolla (R + A) in non-limiting N conditions. During the vegetative stage, the presence of azolla increased allocation of resources to rice shoots without affecting root growth, while in the reproductive stage, it improved panicle architecture, with a 6% increase in length and up to 26% increase in panicle branching. Nevertheless, while this increase in panicle branching in R + A translated into a greater number of grains per plant, grain weight declined. As a result, yields were similar between R and R + A. There was also an azolla-induced increment in several mineral elements in R + A grains, with the notable exception of zinc, which declined by more than 30%. Finally, the presence of azolla altered the expression of several gene families, and in particular, it led to the upregulation of numerous transcription factors from the AP2/ERF, WRKY and NAM families. Interestingly, the presence of azolla also led to the upregulation of several genes (including WRKY transcription factors) involved in resistance to several pathogens and abiotic stresses. Overall, our results suggest that rice-azolla co-cultivation has implications that go beyond N-nutrition for sustainable intensification of rice production.