Transcriptomic Responses to Water Deficit and Nematode Infection in Mycorrhizal Tomato Roots

Abstract

Climate changes include the intensification of drought in many parts of the world, increasing its frequency, severity and duration. However, under natural conditions, environmental stresses do not occur alone, and, in addition, more stressed plants may become more susceptible to attacks by pests and pathogens. Studies on the impact of the arbuscular mycorrhizal (AM) symbiosis on tomato response to water deficit showed that several drought-responsive genes are differentially regulated in AM-colonized tomato plants (roots and leaves) during water deficit. To date, global changes in mycorrhizal tomato root transcripts under water stress conditions have not been yet investigated. Here, changes in root transcriptome in the presence of an AM fungus, with or without water stress (WS) application, have been evaluated in a commercial tomato cultivar already investigated for the water stress response during AM symbiosis. Since root-knot nematodes (RKNs, Meloidogyne incognita) are obligate endoparasites and cause severe yield losses in tomato, the impact of the AM fungal colonization on RKN infection at 7 days post-inoculation was also evaluated. Results offer new information about the response to AM symbiosis, highlighting a functional redundancy for several tomato gene families, as well as on the tomato and fungal genes involved in WS response during symbiosis, underlying the role of the AM fungus. Changes in the expression of tomato genes related to nematode infection during AM symbiosis highlight a role of AM colonization in triggering defense responses against RKN in tomato. Overall, new datasets on the tomato response to an abiotic and biotic stress during AM symbiosis have been obtained, providing useful data for further researches.

Keywords: AM symbiosis; RKN; abiotic stress; stress response; transcriptomics.

FIGURE 1

Differentially expressed tomato genes. DEGs were identified by comparing the expression profiles from treated roots (AM, AM_WS, RKN, RKN_AM) with the equivalent developmental stages of control roots (C) (P ≤ 0.05). Each column represents a treatment.

FIGURE 2

Venn diagram of DEGs (P ≤ 0.05) comparing un-inoculated un-stressed tomato (C) vs. AM, AM_WS, RKN, RKN_AM.

FIGURE 3

Histological analysis of feeding sites induced by Meloidogyne incognita in non-colonized and in Rhizophagus intraradices-colonized tomato roots at 7 days post inoculation. Cross sections (2.5 μm) were stained with toluidine blue and observed at light microscope. (A) Non-colonized gall contained well developed and metabolically active giant cells surrounding the nematode. (B) Giant cells in a AM-colonized gall with an appearance similar to those in non-colonized gall. (C,D) Feeding sites in AM-colonized roots presented giant cells with degraded cytoplasm and clear symptoms of early senescence. Note the presence of numerous hyphae in cortical cells (D,E). Asterisk, giant cell; arrow, nematode; arrowhead, hyphae. Scale bars: 100 μm in (A–D) and 50 μm in (E).