ABSTRACT
The leafhopper family Cicadellidae, comprising over 22,000 species, exhibits a unique behavior of anointing their bodies with excretions containing brochosomes. Brochosomes are synthesized in the distal segment of the Malpighian tubules and serve various functions, including hydrophobic protection and defense against pathogens and predators. In this study, we investigated the distribution, synthesis, and release mechanisms of brochosomes in the rice pest leafhopper Maiestas dorsalis. Using SEM and TEM, we observed brochosomes' consistent coverage on the integument throughout the insect's life cycle. Moreover, we identified four distinct developmental stages of brochosome synthesis within the distal segment of the Malpighian tubules, originating from the Golgi region. Most importantly, our research revealed a novel and highly efficient release mechanism involving the fusion of brochosome-containing vesicles, leading to a rapid and substantial release of brochosomes into the tubule lumen after molting. These findings shed light on the intricate processes of brochosome synthesis and release in leafhoppers, offering valuable insights into their functional significance and ecological role in these fascinating insects.
ABSTRACT
Many insects rely on ancient symbiotic bacterial associations for essential nutrition. Auchenorrhyncha commonly harbor two obligate symbionts: Sulcia (Bacteroidetes) and a proteobacterial partner that supplies essential amino acids lacking in their plant-sap diets. In this study focusing on Maiestas dorsalis, we investigated the distribution and vertical transmission of two obligate symbiotic bacteria, Sulcia and Nasuia, within the leafhopper. Sulcia primarily inhabits the external region of the bacteriome, while Nasuia is restricted to the internal region. Both symbionts progressively infiltrate the ovary through the epithelial plug, ultimately reaching the developing primary oocyte. Furthermore, co-phylogenetic analysis suggests a close correlation between the evolution of Auchenorrhyncha insects and the presence of their obligate symbiotic bacteria. Genomic analysis further unveiled the extreme genome reduction of the obligate symbiotic bacteria, with Sulcia retaining genes involved in basic cellular processes and limited energy synthesis, while Nasuia exhibited further gene loss in replication, transcription, translation, and energy synthesis. However, both symbionts retained the genes for synthesizing the essential amino acids required by the host insect. Our study highlights the coevolutionary dynamics between Sulcia, proteobacterial partners, and their insect hosts, shedding light on the intricate nutritional interactions and evolutionary adaptations in Auchenorrhyncha insects.
ABSTRACT
Effective legume-rhizobia symbiosis depends on efficient nutrient exchange. Rhizobia need to synthesize iron-containing proteins for symbiotic nitrogen fixation (SNF) in nodules, which depends on host plant-mediated iron uptake into the symbiosome. We functionally investigated a pair of vacuolar iron transporter like (VTL) genes, GmVTL1a/b, in soybean (Glycine max) and evaluated their contributions to SNF, including investigations of gene expression patterns, subcellular localization, and mutant phenotypes. Though both GmVTL1a/b genes were specifically expressed in the fixation zone of the nodule, GmVTL1a was the lone member to be localized at the tonoplast of tobacco protoplasts, and shown to facilitate ferrous iron transport in yeast. GmVTL1a targets the symbiosome in infected cells, as verified by in situ immunostaining. Two vtl1 knockout mutants had lower iron concentrations in nodule cell sap and peribacteroid units than in wild-type plants, suggesting that GmVTL1 knockout inhibited iron import into symbiosomes. Furthermore, GmVTL1 knockout minimally affected soybean growth under nonsymbiotic conditions, but dramatically impaired nodule development and SNF activity under nitrogen-limited and rhizobia-inoculation conditions, which eventually led to growth retardation. Taken together, these results demonstrate that GmVTL1a is indispensable for SNF in nodules as a transporter of ferrous iron from the infected root cell cytosol to the symbiosome.
