Abstract
The collection of microorganisms found in the root zone of soil, termed the rhizosphere microbiome, has been shown to impact plant growth and development. Here, we tease apart the function of the cultivable portion of the microbiome from the whole microbiome in retaining plant traits modified through artificial selection on flowering time. Specifically, the whole microbiome associated with earlier flowering time of Arabidopsis thaliana was cultivated on four types of solid media to create cultivated fractions of the microbiome. These cultivated microbiomes were subsequently preserved in glycerol, frozen, and revived to yield a portion of the cultivable fraction to compare (1) whole microbiome, (2) cultivable microbiome, and (3) revived, cultivable microbiome controls on early flowering time. Plants grown in soils inoculated with bacteria grown on 25 % Luria broth and 10 % tryptic soy agar retained the early flowering trait. An increase in leaf biomass with two of the cultivated microbiomes (49.4 and 38.5 %) contrasted the lowered biomass effect of the whole microbiome. Inoculation with the cultivated microbiomes that were cryopreserved in glycerol showed no effect on flowering time or leaf biomass. The results indicate that the cultivable portion of a plant’s microbiome retains the early flowering effect in A. thaliana, but cryopreservation of the cultivated microbiomes disrupts the microbial effects on flowering time. Furthermore, the contrasting effects on leaf biomass (an indirect response from selection on early flowering time), seen with the whole microbiome versus the cultivable portion, suggests versatility in using cultivation methods to modify multiple traits of plants.
Highlights
Several studies have emerged exploring the potential of plantassociated microbiomes to influence a wide range of traits, including growth, disease suppression, stress tolerance, and flowering [1,2,3,4]
We examined an early flowering microbiome enriched over 16 generations of selection in comparison to cultivated and cryopreserved subsets of the early flowering microbiome for their ability to reproduce effects on plant traits in Arabidopsis thaliana
Inoculation of whole early flowering microbiomes into soils of A. thaliana genotype Col led to decreases in leaf biomass
Summary
Several studies have emerged exploring the potential of plantassociated microbiomes to influence a wide range of traits, including growth, disease suppression, stress tolerance, and flowering [1,2,3,4]. More studies are examining the whole microbiome effects on plant traits [7,8,9]. This line of inquiry has led to greater interest in complex host-microbe and microbe-microbe interactions [5, 10, 11]. The complexity of whole microbiomes makes identification of the actual players driving the host responses difficult to decipher. Cultivation of whole microbiomes, without isolation of single strains, is presented here as a method to reduce the complexity of the microbial communities while retaining the key microbial players and preserving their collective functions
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