Driving factors influencing the rhizobacteriome community structure of plants adapted to multiple climatic stressors in edaphic savannas.

The natural variation of multiple abiotic stresses in hyper-seasonal edaphic savanna provides a unique opportunity to study the rhizobacteriome community structure of plants adapted to climate change-like conditions in the humid tropics. In this study, we evaluated changes in soil, plant and rhizobacteriome community structure parameters across seasons (wet and dry) in two edaphic savannas (SV-1 and SV-5) using four dominant plant species. We then examined relationships between rhizobacteriome community structure and soil properties, plant biomass, and conventional and novel root traits. We further hypothesized that plants adapted to the Aripo Savanna had a core rhizobacteriome, which was specific to plant species and related to root foraging traits. Our results showed that cation exchange capacity (CEC) and the concentration of micronutrients (Fe, Cu and B) were the only soil factors that differed across savanna and season, respectively. Plant biomass traits were generally higher in the dry season, with a higher allocation to root growth in SV-5. Root traits were more plastic in SV-5, and network length-distribution was the only root trait which showed a consistent pattern of lower values in the dry season for three of the dominant plant species. Rhizobacterial community compositions were dominated by Proteobacteria and Acidobacteria, as well as WPS-2, which is dominant in extreme environments. We identified a shared core rhizobacteriome across plant species and savannas. Cation exchange capacity was a major driver of rhizobacterial community assemblies across savannas. Savanna-specific drivers of rhizobacterial community assemblies included CEC and Fe for SV-1, and CEC, TDS, NH4+, NO3-, Mn, K, and network length-distribution for SV-5. Plant factors on the microbiome were minimal, and host selectivity was mediated by the seasonal changes. We conclude that edaphoclimatic factors (soil and season) are the key determinants influencing rhizobacteriome community structure in multiple stressed-environments, which are ecologically similar to the Aripo Savanna.

Formamide-based RNA isolation at above zero temperatures from high starch cassava tubers.

INTRODUCTION: Cassava (Manihot esculenta) tubers are a main source of carbohydrate for a large percentage of people in the tropics. However, obtaining RNA from such high starch tubers proves problematic because gelation occurs during standard isolation procedures. In preliminary studies, formamide was used to homogenise tubers at room temperature and no gelation was observed. OBJECTIVES: To develop a simple, reproducible formamide-based procedure for RNA isolation from high starch tissues without the initial use of liquid nitrogen or lyophilisation. A second objective was to determine the impact of storage of formamide homogenates at 4°C on RNA integrity. METHODOLOGY: Tubers were homogenised in 100% formamide at room temperature and stored for 1, 4 or 7 days at 4°C. Homogenates were centrifuged at 14000 × g for 10 min and RNA recovered from the supernatants by isopropanol precipitation followed by dissolution in guanidinium buffer. Protein was removed by standard phenol-chloroform-isoamyl alcohol extraction and RNA recovered by isopropanol precipitation. For immediate RNA isolation, formamide homogenates can be processed without incubation at 4°C. RESULTS: In formamide homogenates a non-gelatinous white pellet was observed which was identified as starch by Lugol's staining. Intact RNA was observed by agarose gel electrophoresis. The RNA was successfully used in downstream RT-PCR reactions. CONCLUSION: Formamide maintained the integrity of the RNA during tissue processing at 25 ± 2°C and storage at 4°C. This room temperature formamide-based RNA isolation procedure met the criteria of simplicity, low-cost, reproducibility and addressed gelation problems associated with high starch tissues.