Abstract
Arbuscular mycorrhizal (AM) fungi are essential elements of soil fertility, plant nutrition and productivity, facilitating soil mineral nutrient uptake. Helianthus annuus is a non-model, widely cultivated species. Here we used an RNA-seq approach for evaluating gene expression variation at early and late stages of mycorrhizal establishment in sunflower roots colonized by the arbuscular fungus Rhizoglomus irregulare. mRNA was isolated from roots of plantlets at 4 and 16 days after inoculation with the fungus. cDNA libraries were built and sequenced with Illumina technology. Differential expression analysis was performed between control and inoculated plants. Overall 726 differentially expressed genes (DEGs) between inoculated and control plants were retrieved. The number of up-regulated DEGs greatly exceeded the number of down-regulated DEGs and this difference increased in later stages of colonization. Several DEGs were specifically involved in known mycorrhizal processes, such as membrane transport, cell wall shaping, and other. We also found previously unidentified mycorrhizal-induced transcripts. The most important DEGs were carefully described in order to hypothesize their roles in AM symbiosis. Our data add a valuable contribution for deciphering biological processes related to beneficial fungi and plant symbiosis, adding an Asteraceae, non-model species for future comparative functional genomics studies.
Highlights
Arbuscular mycorrhizal (AM) symbioses are mutualistic associations between plant roots and soilborne fungi, involving about 80% of land plants
Studies aimed at analysing wide-scale gene reprogramming during the establishment and development of arbuscular mycorrhizal symbioses provided information on the molecular changes occurring in different tissues of a few plant species, such as Medicago truncatula, Lotus japonicus, Pisum sativum, tomato, potato, rice and soybean[9,10,11,12,13,14,15]
The other work on tomato carried out using RNA-seq showed an up-regulation of genes related to photosynthesis, stress response, transport, amino acid synthesis and carbohydrate metabolism functions, and a down-regulation of genes belonging to cell wall, metabolism and ethylene response pathways gene ontology (GO) classes in fruits produced by mycorrhizal plants, compared with non-mycorrhizal ones[33]
Summary
Arbuscular mycorrhizal (AM) symbioses are mutualistic associations between plant roots and soilborne fungi, involving about 80% of land plants. Most of the data reported so far on transcriptome profiles of mycorrhizal plants were obtained by using microarrays or macroarrays, as well as suppression subtractive hybridization and differential display[21,27,32] Such studies provided useful information on mycorrhizal regulated transcripts, limited to the annotated genes available for the different host plant species and tissues. The RNA-seq technology was used to detect whole transcripts in mycorrhizal and non-mycorrhizal Solanum lycopersicum fruits and leaves[33,34] and Oryza sativa and L. japonicus roots[10,14] The use of such a technique showed that important gene functional classes, including post-translational regulation, signalling, transport, biotic and abiotic stresses and hormone metabolism, were differentially regulated in leaves of mycorrhizal tomato plants, compared with non-mycorrhizal ones[34]. Such relationship between susceptibility to AMF and degree of domestication was reported by other studies[47,48] and suggested to be driven by soil characteristics combined with differences in root traits
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