Ethylene-mediated improvement in sucrose accumulation in ripening sugarcane involves increased sink strength

Transcripts libraries were prepared from three sugarcane genotypes with high-sugar (HS), medium-sugar (MS) or low-sugar (LS) content that were treated with ethylene or H2O. The libraries were sequenced with the Illumina paired-end HiSeq platform.Transcriptomic analyses have identified about 160,000 unigenes of which 86000 annotated genes were classified into functional groups associated with carbohydrate metabolism, signaling, localization, transport, hydrolysis, growth, catalytic activity, membrane and storage, suggesting the structural and functional specification, including sucrose accumulation, occurring in maturing internodes. About 25,000 genes were differentially expressed between all genotypes and treatments combined. Genotype had a dominant effect on differential gene expression than ethylene treatment. Sucrose and starch metabolism genes were more responsive to ethylene treatment in low-sugar genotype. Ethylene caused differential gene expression of many stress-related transcription factors, carbohydrate metabolism, hormone metabolism and epigenetic modification. Ethylene-induced expression of ethylene-responsive transcription factors, cytosolic acid- and cell wall-bound invertases, and ATPase was more pronounced in low- than in high-sugar genotype, suggesting an ethylene-stimulated sink activity and consequent increased sucrose accumulation in low-sugar genotype. Two biological replicates each with two technical replicates for each treatment from 3 genotypes were sequenced. The fastq files of the three technical replicates were merged togeher. After quality assessment and data clearance, more than 3 billion (G) reads from each sample were retained as high-quality reads and they were used for subsequent analysis.