Auxin Response Factors (ARFs) are potential mediators of auxin action in tomato response to biotic and abiotic stress (Solanum lycopersicum)

Abstract

Survival biomass production and crop yield are heavily constrained by a wide range of environmental stresses. Several phytohormones among which abscisic acid (ABA), ethylene and salicylic acid (SA) are known to mediate plant responses to these stresses. By contrast, the role of the plant hormone auxin in stress responses remains so far poorly studied. Auxin controls many aspects of plant growth and development, and Auxin Response Factors play a key role in the transcriptional activation or repression of auxin-responsive genes through direct binding to their promoters. As a mean to gain more insight on auxin involvement in a set of biotic and abiotic stress responses in tomato, the present study uncovers the expression pattern of SlARF genes in tomato plants subjected to biotic and abiotic stresses. In silico mining of the RNAseq data available through the public TomExpress web platform, identified several SlARFs as responsive to various pathogen infections induced by bacteria and viruses. Accordingly, sequence analysis revealed that 5' regulatory regions of these SlARFs are enriched in biotic and abiotic stress-responsive cis-elements. Moreover, quantitative qPCR expression analysis revealed that many SlARFs were differentially expressed in tomato leaves and roots under salt, drought and flooding stress conditions. Further pointing to the putative role of SlARFs in stress responses, quantitative qPCR expression studies identified some miRNA precursors as potentially involved in the regulation of their SlARF target genes in roots exposed to salt and drought stresses. These data suggest an active regulation of SlARFs at the post-transcriptional level under stress conditions. Based on the substantial change in the transcript accumulation of several SlARF genes, the data presented in this work strongly support the involvement of auxin in stress responses thus enabling to identify a set of candidate SlARFs as potential mediators of biotic and abiotic stress responses.

Fig 1. SlARFs gene expression in tomato plant leaves exposed to various biotic stresses: Flagellin, Pseudomonas putida, Pseudomonas syringae, Pseudomonas fluorescens, Agrobacterium tumefaciens and Yellow curl virus.

All the data presented here were extracted from TOMPEXPRESS database (http://gbf.toulouse.inra.fr/tomexpress).

Fig 2. GUS activity in DR5::GUS tomato lines in salt or drought stress conditions.

Salt and drought stresses were performed on three week-old tomato plants by adding 250 mM of NaCl or 15% PEG 20000 to the nutrient solution. Black arrows show the location of the GUS activity in the different tissues analyzed.

Fig 3. SlARFs gene expression under salt, drought and flooding conditions.

Values are mean ± SD of three biological replicates. White bars represent the expression of stress marker: CI7 for salt and drought stresses (Leaves & Roots), ACO1 in flooded leaves and PDC1 in flooded roots. Stars (*) indicate the statistical significance (p<0,05) using Student’s t-test.

Fig 4. GUS activity in pARF8A::GUS tomato lines in salt or drought stress conditions.

Salt and drought stresses were performed on three week-old tomato plants by adding 250 mM of NaCl or 15% PEG 20000 to the nutrient solution. Black arrows show the location of the GUS activity in the different tissues analyzed.

Fig 5. GUS activity in pARF10A::GUS tomato lines in salt or drought stress conditions.

Salt and drought stresses were performed on three week-old tomato plants by adding 250 mM of NaCl or 15% PEG 20000 to the nutrient solution. Black arrows show the location of the GUS activity in the different tissues analyzed.

Fig 6. SlARF10A and miR160 expression under salt and drought stress conditions.

Values are mean ± SD of three biological replicates. Stars (*) indicate the statistical significance (p<0,05) using Student’s t-test.

Fig 7. SlARF8A and miR167s (miR167a, miR167b, miR167c, miR167d) expression under salt and drought stress conditions.

Values are mean ± SD of three biological replicates. Stars (*) indicate the statistical significance (p<0,05) using Student’s t-test.