Abstract
Root-root interactions are much more sophisticated than previously thought, yet the mechanisms of belowground neighbor perception remain largely obscure. Genome-wide transcriptome analyses allow detailed insight into plant reactions to environmental cues. A root interaction trial was set up to explore both morphological and whole genome transcriptional responses in roots of Arabidopsis thaliana in the presence or absence of an inferior competitor, Hieracium pilosella. Neighbor perception was indicated by Arabidopsis roots predominantly growing away from the neighbor (segregation), while solitary plants placed more roots toward the middle of the pot. Total biomass remained unaffected. Database comparisons in transcriptome analysis revealed considerable similarity between Arabidopsis root reactions to neighbors and reactions to pathogens. Detailed analyses of the functional category “biotic stress” using MapMan tools found the sub-category “pathogenesis-related proteins” highly significantly induced. A comparison to a study on intraspecific competition brought forward a core of genes consistently involved in reactions to neighbor roots. We conclude that beyond resource depletion roots perceive neighboring roots or their associated microorganisms by a relatively uniform mechanism that involves the strong induction of pathogenesis-related proteins. In an ecological context the findings reveal that belowground neighbor detection may occur independently of resource depletion, allowing for a time advantage for the root to prepare for potential interactions.
Highlights
Information on neighboring organisms is crucial to a plant, because neighbors are potential interaction partners both in competition and facilitation (Cahill et al, 2010; Faget et al, 2013)
Root distribution varied significantly between treatments with control plants placing more of their root biomass in the center of the pot [log2(Root Mass Ratio) > 0] while plants exposed to neighbors placed more root biomass toward the margin of the pot [log2(Root Mass Ratio) < 0; Figure 2C]
ALTERATION OF ROOT DISTRIBUTION AS AVOIDANCE OF POTENTIAL COMPETITION We found that in the presence of a neighbor, A. thaliana places more roots toward the margin than toward the center of the pot (Table 1, Figure 2), i.e., the neighbor root is avoided by root segregation (Schenk et al, 1999)
Summary
Information on neighboring organisms is crucial to a plant, because neighbors are potential interaction partners both in competition and facilitation (Cahill et al, 2010; Faget et al, 2013). It became clear that roots can perceive each other and as a consequence the plants increase allocation to roots. This finding triggered intense research on root-root interactions that comprises several related ideas and research topics namely (i) distinction of kin and stranger roots (stranger recognition) (ii) distinction of own and foreign roots (self/non-self recognition) (iii) perception of the presence/absence of neighbor roots (neighbor perception). Lacustris increased allocation to roots when sharing a pot with strangers as opposed to siblings (Dudley and File, 2007; Bhatt et al, 2011). Root exuded proteins and metabolites were found to differ depending on neighbor identity (Badri et al, 2012). Some components of plant exudates have already been found to be perceived by some specialized www.frontiersin.org
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