Abstract
Ethylene is a phytohormone involved in the regulation of several aspects of plant development and in responses to biotic and abiotic stress. The effects of exogenous application of ethylene to sugarcane plants are well characterized as growth inhibition of immature internodes and stimulation of sucrose accumulation. However, the molecular network underlying the control of ethylene biosynthesis in sugarcane remains largely unknown. The chemical reaction catalyzed by 1-aminocyclopropane-1-carboxylic acid synthase (ACS) is an important rate-limiting step that regulates ethylene production in plants. In this work, using a yeast one-hybrid approach, we identified three basic helix-loop-helix (bHLH) transcription factors, homologs of Arabidopsis FBH (FLOWERING BHLH), that bind to the promoter of ScACS2 (Sugarcane ACS2), a sugarcane type 3 ACS isozyme gene. Protein-protein interaction assays showed that sugarcane FBH1 (ScFBH1), ScFBH2, and ScFBH3 form homo- and heterodimers in the nucleus. Gene expression analysis revealed that ScFBHs and ScACS2 transcripts are more abundant in maturing internodes during afternoon and night. In addition, Arabidopsis functional analysis demonstrated that FBH controls ethylene production by regulating transcript levels of ACS7, a homolog of ScACS2. These results indicate that ScFBHs transcriptionally regulate ethylene biosynthesis in maturing internodes of sugarcane.
Highlights
Sugarcane (Saccharum spp.) is a monocot that accumulates large quantities of sucrose in the culm, reaching concentrations of up to 650 mM (Welbaum and Meinzer, 1990) or 18% of fresh weight (Inman-Bamber et al, 2011)
We identified three basic helix-loophelix (bHLH) transcription factors (ScFBH1, ScFBH2, and ScFBH3), which are phylogenetically related to Arabidopsis FBHs, dimerize in cell nucleus, and bind to the ScACS2 promoter, activating its expression
As a first step to identify the transcription factors able to bind to the ScACS2 promoter, we confirmed the transcriptional activity of the promoter by transient transformation of a promScACS2:GUS construct into in vitro-grown sugarcane leaves and calli by particle bombardment
Summary
Sugarcane (Saccharum spp.) is a monocot that accumulates large quantities of sucrose in the culm, reaching concentrations of up to 650 mM (Welbaum and Meinzer, 1990) or 18% of fresh weight (Inman-Bamber et al, 2011). Transcriptomic analysis has identified ethylene as a potential regulator of sugar storage in the internodes (Papini-Terzi et al, 2009; Cunha et al, 2017).
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