Using microbial inoculants to enhance plant health is promising for crop improvement. However, for success, knowledge of how different cultivars within a crop species select and respond to the root microbiome is critical. The aims of this study were to 1) determine the contribution of tomato genotype to the tomato root bacterial microbiome, and 2) investigate whether closely related tomato genotypes differ in their selection of, and response to, root endophytes. We used 16S rRNA amplicon sequencing to examine the root bacterial communities of six Solanum lycopersicum (domesticated tomato) and two Solanum pimpinellifolium (wild tomato) accessions. We found that across tomatoes, both the root endosphere and rhizosphere were impacted by genotype. Genotype accounted for 10% of the variation in root microbiota. Two bacterial families, Bacillaceae and Rhizobiaceae, were significantly enriched in the root endosphere in at least six of the eight tomato genotypes. To investigate whether closely related tomato genotypes differed in selection of these endosphere-enriched taxa, we profiled the root endosphere of 20 recombinant inbred lines (RILs) derived from two of the genotypes. The abundance of Bacillaceae and Rhizobiaceae varied quantitatively in the root endosphere of the RILs. Inoculation of 16 RILs with a Bacillaceae isolate identified from the root endosphere of field grown tomatoes showed that RIL responses, in terms of shoot and root growth, varied from less than 5% growth enhancement to over 40%. Our data show that tomato genotypes have distinct but overlapping root bacterial microbiomes and respond differently to specific bacterial endophytes.
Plant disease limits crop production, and host genetic resistance is a major means of control. Plant pathogenic Ralstonia causes bacterial wilt disease and is best controlled with resistant varieties. Tomato wilt resistance is multigenic, yet the mechanisms of resistance remain largely unknown. We combined metaRNAseq analysis and functional experiments to identify core Ralstonia‐responsive genes and the corresponding biological mechanisms in wilt‐resistant and wilt‐susceptible tomatoes. While trade‐offs between growth and defence are common in plants, wilt‐resistant plants activated both defence responses and growth processes. Measurements of innate immunity and growth, including reactive oxygen species production and root system growth, respectively, validated that resistant plants executed defence‐related processes at the same time they increased root growth. In contrast, in wilt‐susceptible plants roots senesced and root surface area declined following Ralstonia inoculation. Wilt‐resistant plants repressed genes predicted to negatively regulate water stress tolerance, while susceptible plants repressed genes predicted to promote water stress tolerance. Our results suggest that wilt‐resistant plants can simultaneously promote growth and defence by investing in resources that act in both processes. Infected susceptible plants activate defences, but fail to grow and so succumb to Ralstonia, likely because they cannot tolerate the water stress induced by vascular wilt.
Object detection is an essential function of the visual system. Although the visual cortex plays an important role in object detection, the superior colliculus can support detection when the visual cortex is ablated or silenced. Moreover, it has been shown that superficial layers of mouse SC (sSC) encode visual features of complex objects, and that this code is not inherited from the primary visual cortex. This suggests that mouse sSC may provide a significant contribution to complex object vision. Here, we use optogenetics to show that mouse sSC is causally involved in figure detection based on differences in figure contrast, orientation and phase. Additionally, our neural recordings show that in mouse sSC, image elements that belong to a figure elicit stronger activity than those same elements when they are part of the background. The discriminability of this neural code is higher for correct trials than incorrect trials. Our results provide new insight into the behavioral relevance of the visual processing that takes place in sSC.
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