Transcriptional profiles of sunflower roots during mycorrhizal colonization as revealed by RNA-SEQ

Sunflower (Helianthus annuus L.) is an important crop cultivated worldwide and represents a non-model plant species, whose mycorrhizal status was recently assessed in wild accessions, cultivars and inbred lines1. Previous sunflower transcriptome analyses revealed gene differ-ential expression in response to biotic/abiotic stresses2, while no data are available on changes induced by arbuscular mycorrhizal (AM) fungi. Here, for the first time, an RNAseq approach was used to investigate transcriptional changes in mycorrhizal versus nonmycorrhi-zal sunflower roots and gene differential expression at early and late stages of mycorrhizal establishment. Sunflower plantlets were inoculated with the AM symbiont Rhizoglomus irregulare and total RNA was isolated from roots 4 and 16 days after inoculation. Twelve cDNA libraries were built and sequenced by Illumina technology. A de novo transcriptome was established by assem-bling Illumina reads and annotating contigs. After quantitative analyses by mapping reads against the de novo assembled transcriptome 1,037 differentially expressed putative tran-scripts (DEs) between mycorrhizal and control plants were identified. The number of over-expressed DEs was much higher than under-expressed ones, increasing over time. Gene On-tology analyses showed that several DEs were specifically involved in known mycorrhizal pro-cesses, such as membrane transport (ABC transporters, ammonium transporters), cell wall shaping (subtilisins, ascorbate oxidases), gene networking (DELLA, ERF) and defense response (germin-like protein, pathogen-related proteins). We also identified new mycorrhizal-induced putative transcripts, such as BAHD-acyltransferase and Nph3. This work provides novel data on gene expression during the establishment of AM symbiosis in a non-model plant species, useful for future comparative functional genomics analyses. References: 1 Turrini A., Giordani T., Avio L., Natali L., Giovannetti M., Cavallini A. (2016). Large variation in mycorrhizal colonization among wild accessions, cultivars, and inbreds of sunflower (Helian-thus annuus L.). EUPHYTICA 207: 331-342 2 Ramu V., Anjugam P., Venkategowda R., Basavaiah M., Makarla U., Muthappa S. (2016). Transcriptome analysis of sunflower genotypes with contrasting oxidative stress tolerance reveals Individual- and combined-biotic and abiotic stress tolerance mechanisms. PLOSone 11(6): e0157522. doi:10.1371/journal.pone.0157522