Background: Azolla is a small floating fern living in symbiosis with nitrogen-fixing cyanobacteria and provides a variety of important ecosystem benefits. Previous studies have presented that Azolla harbors diverse bacteria that may play a key role in host fitness and productivity. However, the characteristics of endophytic bacteria inhabiting the phyllosphere of different species of Azolla have not yet been fully understood. Results: In this study, the 16S ribosomal DNA (rDNA) V5-V7 region of bacteria was determined by Illumina high-throughput sequencing platform to study the diversity and richness of endophytic bacterial communities in the phyllosphere of five Azolla species collected from different countries. A total of 1150 operational taxonomic units (OTUs) were detected for the endophytic bacteria community. According to the α diversity indices, the diversity of bacteria was ordered as Azolla imbricata > A. pinnata > A. filiculoides > A. mexicana > A. caroliniana. The PCoA results displayed that the bacterial communities of A. mexicana and A. caroliniana shared the highest similarity, followed by the similarity between A. pinnata and A. imbricata, and they were significantly distinct from the community of A. filiculoides. The dominant bacteria of Azolla mainly belonged to the phylum of Proteobacteria, followed by Actinobacteria, Chlorobillobacteria, and Firmicutes. In detail, the relative abundance of Proteobacteria in A. imbricata was 52.23%, whereas it was more than 80.00% in the other four species of Azolla. Notably, Herbaspirillum (45.91%, 44.08%) and Methylophilus (29.97%, 37.96%) were the main genera inhabiting A. mexicana and A. caroliniana respectively. Ferrovibrio (18.54%) and Rhizobium (16.68%) were the dominant genera inhabiting A. filiculoides. The group of unidentified genera (41.63%, 44.92%) consisted most of the bacteria in A. imbricata and A. pinnata respectively. Further analysis suggested that the significant different bacteria identified in LDA Effect Size analysis existed Azolla species-specific patterns. Conclusions: In summary, all results suggested that the diversity and composition of the endophytic bacterial communities were different in Azolla species.

Cortical microtubules guide the direction and deposition of cellulose microfibrils to build the cell wall, which in turn influences cell expansion and plant morphogenesis. In the model plant Arabidopsis thaliana (Arabidopsis), petal is a relatively simple organ that contains distinct epidermal cells, such as specialized conical cells in the adaxial epidermis and relatively flat cells with several lobes in the abaxial epidermis. In the past two decades, the Arabidopsis petal has become a model experimental system for studying cell expansion and organ morphogenesis, because petals are dispensable for plant growth and reproduction. Recent advances have expanded the role of microtubule organization in modulating petal anisotropic shape formation and conical cell shaping during petal morphogenesis. Here, we summarize recent studies showing that in Arabidopsis, several genes, such as SPIKE1, Rho of plant (ROP) GTPases, and IPGA1, play critical roles in microtubule organization and cell expansion in the abaxial epidermis during petal morphogenesis. Moreover, we summarize the live-confocal imaging studies of Arabidopsis conical cells in the adaxial epidermis, which have emerged as a new cellular model. We discuss the microtubule organization pattern during conical cell shaping. Finally, we propose future directions regarding the study of petal morphogenesis and conical cell shaping.

Background: The aquatic fern Azolla grows rapidly, produces nutrient-rich biomass, and adapts well ecologically due to symbiotic interactions with phyllospheric microorganisms. Azolla imbricata (Aim) and Azolla pinnata (Api) are valuable for biofertilization and phytoremediation, with their ecological differences potentially influenced by species-specific microbial partnerships. This study examines their phyllospheric microbiomes under controlled conditions to explore adaptive strategies. Method and Results: High-throughput metagenomic sequencing identified 10,857 bacteria, 986 eukaryotes. Proteobacteria dominated, particularly Burkholderiales, with higher abundance in Aim. Api exhibited greater Cyanobacteria abundance, especially Nostocaceae (genus Trichormus). Streptophyta constituted over 90% of fungal communities in both species. LEfSe analysis highlighted unique taxa in each species, including enriched Magnoliopsida and Bacillariophyta in Aim, while Api had more Marchantia and Streptophyta. KEGG pathway analysis identified ribosome, oxidative phosphorylation, photosynthesis, quorum sensing, and two-component systems among the most enriched pathways. Resistance gene analysis showed Aim had higher levels of cmlA9, qacEdelta1, tetD, and ANT3-Ii-AAC6-IId_fusion_protein, while Api had more AAC6-IIa. Conclusions: Aim’s enrichment in Proteobacteria may enhance resilience, while Api’s nitrogen-fixing Cyanobacteria suggest distinct nitrogen management. Functional and resistance gene differences highlight ecological adaptability, providing insights for optimizing Azolla’s agricultural potential.