Figure 1.
Effect of earthworm casts on plant growth in in vitro experiments.
Experimental in vitro device with Oryza sativa in presence of (A) casts of Aporrectodea caliginosa or (B) equivalent weight of control soil enclosed into a nylon membrane. Effect of Aporrectodea caliginosa’s casts on total biomass production of (C) Lolium perenne and (D) Oryza sativa. Effect of Aporrectodea caliginosa’s casts on root length of (E) Lolium perenne and (F) Oryza sativa. Effect of Aporrectodea caliginosa’s casts on the number of lateral roots of (G) Lolium perenne and (H) Oryza sativa. Means±s.e., n = 10 per treatment, different letters indicates a significant difference, Tukey HSD, P<0.05.
Figure 2.
Effects of Apporectodea caliginosa on the growth of Arabidopsis thaliana cv. Columbia and aux1-7;axr4-2 mutant.
(A) Picture of Arabidospis thaliana at three weeks after sowing. Effect of the presence of Aporrectodea caliginosa on (B) total biomass production, (C) root length and (D) the number of lateral roots. Means ± s.e., n = 5 per treatment, different letters indicates a significant difference, Tukey HSD, P<0.05.
Table 1.
Impact of the factor “earthworm” and “genotype” on biomass and morphological parameters of Arabidopsis thaliana, estimated in a two-ways ANOVA.
Figure 3.
Validation of the results obtained in transcriptomic analysis by real-time polymerase chain reaction (qPCR).
Six genes were selected from the 59 differentially expressed genes obtained by transcriptomic analysis (Table 2). Transcript abundance was standardized by reporting it to the constitutive At5g11770 gene. A log base 2 transformation was applied on the average transcript abundance level to obtain data similar to the transformed microarray data.
Figure 4.
Functions of the 59 Arabidopsis thaliana genes differentially expressed in the presence of earthworms.
Functional classification was established according to http://www.arabidopsis.org and the related publications.
Figure 5.
Comparison between genes modulated in the presence of earthworms with other transcriptomic studies.
Among our 59 genes, 56 upregulated genes were found in Genvestigator database (in column). We then select a list of 60 studies (in line), among 54 922 referenced in Genevestigator, exhibiting the most similar directional changes with the 56 genes of our study by choosing the “mosaic” with the highest number of red squares (higher transcript abundance in the treatment as compared with control). Green color is corresponding to a lower transcript abundance for the treatment as compared with the control, and red color is corresponding to higher transcript abundance. Color intensity is corresponding to the fold change in gene transcript abundance.
Table 2.
List of the genes of Arabidopsis thaliana differentially expressed in the presence/absence of the earthworm Aporrectodea caliginosa in two replicated experiments.
Figure 6.
Model explaining contrasting effects of the earthworm Aporrectodea caliginosa on Arabidopsis thaliana.
This model explains positive as well as negative effects on Arabidopsis thaliana wild type and mutant for auxin transport (aux1-7 axr4-2). Note that the effect of an exogenous auxin supply in the presence of earthworms is dependent on the initial auxin concentration in root cells.