Silencing a key gene of the common symbiosis pathway in Nicotiana attenuata specifically impairs arbuscular mycorrhizal infection without influencing the root‐associated microbiome or plant growth

Abstract

While the biochemical function of calcium and calmodulin-dependent protein kinase (CCaMK) is well studied, and plants impaired in the expression of CCaMK are known not to be infected by arbuscular mycorrhizal fungi (AMF) in glasshouse studies, the whole-plant and ecological consequences of CCaMK silencing are not well understood. Here we show that three independently transformed lines of Nicotiana attenuata plants silenced in CCaMK (irCCaMK) are neither infected by Rhizophagus irregularis in the glasshouse nor by native fungal inoculum in the field. The overall fungal community of field-grown roots did not differ significantly among empty vector (EV) and the transgenic lines, and the bacterial communities only showed minor differences, as revealed by the alpha-diversity parameters of bacterial OTUs, which were higher in EV plants compared with two of the three transformed lines, while beta-diversity parameters did not differ. Furthermore, growth and fitness parameters were similar in the glasshouse and field. Herbivory-inducible and basal levels of salicylic acid, jasmonic acid and abscisic acid did not differ among the genotypes, suggesting that activation of the classical defence pathways are not affected by CCaMK silencing. Based on these results, we conclude that silencing of CCaMK has few, if any, non-target effects.

Nicotiana attenuata's capacity to interact with arbuscular mycorrhiza alters its competitive ability and elicits major changes in the leaf transcriptome

“…The most abundant species colonizing N. attenuata roots were identified as F. mosseae and R. irregularis (Figure ) with strains related to Rhizophagus dominating the community. This composition of fungal species is similar to that reported from field grown‐plants from the same soil in the plant's native habitat (Groten et al ), and hence mimics natural conditions well.…”

“…This fire‐chasing annual plant shows synchronized mass germination from long‐lived dormant seed‐banks and monocultural growth with high intra‐specific competition after fires in its native habitat (Baldwin and Morse ; Baldwin et al ). An RNAi line, silenced in the expression of its calcium‐ and calmodulin‐dependent protein kinase (inverted repeat (ir) CCaMK ), a key enzyme facilitating the interaction with AMF, does not show arbuscule formation when grown in the field in native habitats and the glasshouse, and when grown in single pots, develops in a manner indistinguishable from wild type plants (Groten et al ), a prerequisite for comparative studies (Rillig et al ). Many additional genes (e.g.…”

Specificity of root microbiomes in native‐grown Nicotiana attenuata and plant responses to UVB increase Deinococcus colonization

“…, ; Groten et al . ), we found the phylum Deinococcus–Thermus in all root samples of native field‐grown N. attenuata irrespective of plant developmental stages, and genotypes and field seasons; although relative abundance varied and ranged from 0.3 to 22%, except for Gate location with an abundance of about 50%.…”

“…, ; Groten et al . ), and we speculated that the local soil environment has a stronger effect on the plant's microbiome than the genotype. In this work, we expanded our analysis to the seedborne microbiome to evaluate whether a core group of microbes is transmitted to the offspring and serves as primary source for root colonization, and characterized the root microbiota of N. attenuata plants from different natural populations grown at different locations in their native habitat.…”

“…; Groten et al . ). The studies revealed that the microbiomes of plants grown on the same field plot were sufficiently variable to mask any effects of the loss of jasmonate and mycorrhizal signalling pathways from the host (Santhanam et al .…”