How do roots respond to osmotic stress? A transcriptomic approach to address this question in a non-model crop

Drought is a complex phenomenon that is relevant for many crops. Performing high-throughput transcriptomics in non-model crops is challenging. The non-model crop where our workflow has been tested on is banana (Musa spp.), which ranks among the top ten staple foods (total production over 145 million tons in 2013 (FAOstat)[1]). Bananas need vast amounts of water and even mild-drought conditions are responsible for considerable yield losses[2]. To characterize drought in the roots of different banana genotypes, we designed a lab model based on osmotic stress (5% PEG treatment for 3 days) and performed mRNA-seq analysis[3]. Using Illumina technology, 18 cDNA libraries were sequenced producing around 568 million high quality reads, of which 70-84% were mapped to the diploid reference genome[4]. We show that the applied stress leads to a drop in energy levels inducing a metabolic shift towards (i) higher oxidative respiration, (ii) alternative respiration and (iii) fermentation. We also analyzed the expression patterns of paralogous genes belonging to the same gene families and detected possible cases of sub-functionalization

Differential root transcriptomics in a polyploid non-model crop: the importance of respiration during osmotic stress

To explore the transcriptomic global response to osmotic stress in roots, 18 mRNA-seq libraries were generated from three triploid banana genotypes grown under mild osmotic stress (5% PEG) and control conditions. Illumina sequencing produced 568 million high quality reads, of which 70–84% were mapped to the banana diploid reference genome. Using different uni- and multivariate statistics, 92 genes were commonly identified as differentially expressed in the three genotypes. Using our in house workflow to analyze GO enriched and underlying biochemical pathways, we present the general processes affected by mild osmotic stress in the root and focus subsequently on the most significantly overrepresented classes associated with: respiration, glycolysis and fermentation. We hypothesize that in fast growing and oxygen demanding tissues, mild osmotic stress leads to a lower energy level, which induces a metabolic shift towards (i) a higher oxidative respiration, (ii) alternative respiration and (iii) fermentation. To confirm the mRNA-seq results, a subset of twenty up-regulated transcripts were further analysed by RT-qPCR in an independent experiment at three different time points. The identification and annotation of this set of genes provides a valuable resource to understand the importance of energy sensing during mild osmotic stress

Effect of paleopolyploidy and allopolyploidy on gene expression in banana

Open Access JournalBananas (Musa spp.) are an important crop worldwide. Most modern cultivars resulted from a complex polyploidization history that comprised three whole genome duplications (WGDs) shaping the haploid Musa genome, followed by inter- and intra-specific crosses between Musa acuminata and M. balbisiana (A and B genome, respectively). Unresolved hybridizations finally led to banana diversification into several autotriploid (AAA) and allotriploid cultivars (AAB and ABB). Using transcriptomic data, we investigated the impact of the genome structure on gene expression patterns in roots of 12 different triploid genotypes covering AAA, AAB and ABB subgenome constitutions

Gene expression atlas of fruit ripening and transcriptome assembly from RNA-seq data in octoploid strawberry (Fragaria × ananassa)

RNA-seq has been used to perform global expression analysis of the achene and the receptacle at four stages of fruit ripening, and of the roots and leaves of strawberry (Fragaria × ananassa). About 967 million reads and 191 Gb of sequence were produced, using Illumina sequencing. Mapping the reads in the related genome of the wild diploid Fragaria vesca revealed differences between the achene and receptacle development program, and reinforced the role played by ethylene in the ripening receptacle. For the strawberry transcriptome assembly, a de novo strategy was followed, generating separate assemblies for each of the ten tissues and stages sampled. The Trinity program was used for these assemblies, resulting in over 1.4 M isoforms. Filtering by a threshold of 0.3 FPKM, and doing Blastx (E-value < 1 e-30) against the UniProt database of plants reduced the number to 472,476 isoforms. Their assembly with the MIRA program (90% homology) resulted in 26,087 contigs. From these, 91.34 percent showed high homology to Fragaria vesca genes and 87.30 percent Fragaria iinumae (BlastN E-value < 1 e-100). Mapping back the reads on the MIRA contigs identified polymorphisms at nucleotide level, using FREEBAYES, as well as estimate their relative abundance in each sample

Banana triploid cultivars under osmotic stress conditions

Different banana (Musa spp.) genotypes, composed of auto and allo-triploids, were phenotypically evaluated according to their performance in an in vitro osmotic stress test (5% PEG treatment for 21 days