Insights into Ethylene-Driven Response during Sugarcane Ripening: A Combined Transcriptome and Hormone Profile Approach

Ethylene-based ripeners are commonly applied to sugarcane fields to accelerate maturation or to delay flowering, with positive impact on sucrose yield and harvest management. Apart from phenotypic and physiological changes during ripening, the role of ethylene at the transcriptional level remains unknown. A transcriptome analysis combined with hormone profiling of sugarcane plants cv. IACSP95-5000 (high sucrose yield and mid-late maturing) exposed to an ethylene-releasing compound (ethephon) and ethylene biosynthesis inhibitor (AVG) prior to ripening led to ethylene-modulated gene expression and hormone crosstalk investigation. A significant proportion of differentially expressed genes (approximately 20 %) was found within hormone metabolism, transcription and signaling categories, coherent with the role of ethylene as triggers of multiple hormone signal cascades. There was a correlation between hormone levels and transcriptional changes of hormone-related genes, inferred by orthology with the model plant Arabidopsis, confirming the effect of ethylene on altering hormone homeostasis. Interestingly, a detailed analysis of gene expression suggests that only the upper internode tissue was prone to respond to ethylene, showing a high induction of genes involved in ethylene biosynthesis and signaling. Besides, ethylene seems to act synergistically with jasmonate, ABA, and cytokinin, which levels and marker genes increased upon ethephon exposure, and antagonistically with gibberellin, probably mediated by DELLA. Our analysis allowed not only the identification of potential ethylene target genes, but also the characterization of hormone status during ripening, providing insights into the action of ethylene in the site of sucrose accumulation. A molecular model of ethylene interplay with other hormones was devised.