Azomite, a volcanic ash-based fertilizer modulates gene expression during photomorphogenesis through phyB-dependent and independent pathways

Abstract

Azomite is a lightly weathered dacitic (rhyolitic) tuff breccia (DTB), it is silicon-based with over 70 minerals and trace elements (micronutrients). In previous studies, application of Azomite increased greenhouse tomato production. In the tomato root endosome, Azomite caused functional shifts from higher abundance of microbes involved in metabolism of 2- to 4- carbon compounds to higher levels of microbes involved in carbohydrate metabolism. This suggested a possible increase in carbohydrate production and shift in exudates involved in microbial recruitment. Parallel studies with 4-day old Arabidopsis seedlings revealed that photosynthetically active radiation was required for Azomite-induced increase in both hypocotyl length and cotyledon area. These data suggested that Azomite may influence growth through changes in photosynthesis, leading to carbohydrate-enriched root exudates and increased growth. Here, we present RNAseq analysis in response to Azomite of 4-day old Arabidopsis seedlings grown either in continuous darkness (Dc) or under continuous red-light (Rc). Significant changes in genes involved in carbon assimilation and nutrient uptake, amongst other functional pathway categories are reported. Comparison with phyB (phytochrome B, red-light photoreceptor) mutant seedlings is shown to determine the overlap between phyB-regulated genes and Azomite-responsive genes. Two concentrations, 0.5 g and 1.0 g of Azomite were included because our previous results with tomato and Arabidopsis exhibited a dose-dependent response. Several genes are identified as responding differentially, including SUBERMAN, a myb-family transcription factor that regulates suberization of the root endodermis. This study advances our understanding of how complex mixtures of micronutrients such as Azomite influence gene expression during plant growth and development.