Bacillus for Plant Growth Promotion and Stress Resilience: What Have We Learned?

The rhizosphere is a thin film of soil that surrounds plant roots and the primary location of nutrient uptake, and is where important physiological, chemical, and biological activities are occurring. Many microbes invade the rhizosphere and have the capacity to promote plant growth and health. Bacillus spp. is the most prominent plant growth promoting rhizobacteria due to its ability to form long-lived, stress-tolerant spores. Bacillus-plant interactions are driven by chemical languages constructed by a wide spectrum of metabolites and lead to enhanced plant growth and defenses. Thus, this review is a synthesis and a critical assessment of the current literature on the application of Bacillus spp. in agriculture, highlighting gaps that remain to be explored to improve and expand on the Bacillus-based biostimulants. Furthermore, we suggest that omics sciences, with a focus on metabolomics, offer unique opportunities to illuminate the chemical intercommunications between Bacillus and plants, to elucidate biochemical and molecular details on modes of action of Bacillus-based formulations, to generate more actionable insights on cellular and molecular events that explain the Bacillus-induced growth promotion and stress resilience in plants.

Selection and evaluation of housekeeping genes as endogenous controls for quantification of mRNA transcripts in Theileria parva using quantitative real-time polymerase chain reaction (qPCR).

The reliability of any quantitative real-time polymerase chain reaction (qPCR) experiment can be seriously compromised by variations between samples as well as between PCR runs. This usually result from errors in sample quantification, especially with samples that are obtained from different individuals and tissues and have been collected at various time intervals. Errors also arise from differences in qPCR efficiency between assays performed simultaneously to target multiple genes on the same plate. Consequently, the derived quantitative data for the target genes become distorted. To avoid this grievous error, an endogenous control, with relatively constant transcription levels in the target individual or tissue, is included in the qPCR assay to normalize target gene expression levels in the analysis. Several housekeeping genes (HKGs) have been used as endogenous controls in quantification studies of mRNA transcripts; however, there is no record in the literature of the evaluation of these genes for the tick-borne protozoan parasite, Theileria parva. Importantly, the expression of these genes should be invariable between different T. parva stocks, ideally under different experimental conditions, to gain extensive application in gene expression studies of this parasite. Thus, the expression of several widely used HKGs was evaluated in this study, including the genes encoding ß-actin, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), 28S rRNA, cytochrome b and fructose-2.6-biphosphate aldolase (F6P) proteins. The qPCR analysis revealed that the expression of genes encoding cytochrome b, F6P and GAPDH varied considerably between the two T. parva stocks investigated, the cattle-derived T. parva Muguga and the buffalo-derived T. parva 7014. 28S rRNA and ß-actin gene expression was the most stable; thus, these genes were considered suitable candidates to be used as endogenous control genes for mRNA quantification studies in T. parva.