Abstract
The effects of ethephon as a sugarcane ripener are attributed to ethylene. However, the role of this phytohormone at the molecular level is unknown. We performed a transcriptome analysis combined with the evaluation of sucrose metabolism and hormone profiling of sugarcane plants sprayed with ethephon or aminoethoxyvinylglycine (AVG), an ethylene inhibitor, at the onset of ripening. The differential response between ethephon and AVG on sucrose level and sucrose synthase activity in internodes indicates ethylene as a potential regulator of sink strength. The correlation between hormone levels and transcriptional changes suggests ethylene as a trigger of multiple hormone signal cascades, with approximately 18% of differentially expressed genes involved in hormone biosynthesis, metabolism, signalling, and response. A defence response elicited in leaves favoured salicylic acid over the ethylene/jasmonic acid pathway, while the upper internode was prone to respond to ethylene with strong stimuli on ethylene biosynthesis and signalling genes. Besides, ethylene acted synergistically with abscisic acid, another ripening factor, and antagonistically with gibberellin and auxin. We identified potential ethylene target genes and characterized the hormonal status during ripening, providing insights into the action of ethylene at the site of sucrose accumulation. A molecular model of ethylene interplay with other hormones is proposed.
Highlights
Ethephon stimulates sucrose accumulation in immature internodes accompanied of shoot growth inhibition[7,9]
The effect of ethephon and AVG on sugar accumulation was verified through quantification of sucrose and hexose contents on a biomass basis in leaf and culm tissues sampled at the beginning of experimentation and at harvest (32 days after chemical application (DAA)) (Fig. 1)
Enzyme activities were statistically different between chemicals for sucrose-phosphate synthase (SPS, Fig. 2e), sucrose synthase (SuSy, Fig. 2f), and soluble acid invertase (SAI, Fig. 2g) in middle internodes, while neutral invertase (NI) was altered in both leaves and middle internodes (Fig. 2d,h)
Summary
An ethylene releasing compound, was the first growth regulator (early 1960s) used for crop management and post-harvest quality in a wide range of agricultural, horticultural and forestry species[8]. Other growth regulator is the aminoethoxyvinylglycine (AVG), a potent antagonist of ethylene that interferes with the hormone biosynthesis[10], representing a powerful tool for ethylene research[10,11]. A better understanding of the regulation of sucrose accumulation, biomass production, and stress tolerance represents major breakthroughs for the sugarcane industry in an era of challenges, such as climate change, water scarcity, and high energy demand. The aim of this study was to investigate ethylene-modulated gene expression in a high sucrose yield and mid-late season maturing sugarcane cultivar through the application of ethephon and AVG at the onset of ripening. This study advanced our scientific knowledge on ethylene-driven processes and pointed novel targets for future genome-wide assisted-selection and biotechnology to foster the production of elite cultivars
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