Transcriptome analysis of Para rubber tree (H. brasiliensis) seedlings under ethylene stimulation

Background Natural rubber (cis-1,4-polyioprene, NR) is an indispensable industrial raw material obtained from the Para rubber tree (H. brasiliensis). Natural rubber cannot be replaced by synthetic rubber compounds because of the superior resilience, elasticity, abrasion resistance, efficient heat dispersion, and impact resistance of NR. In NR production, latex is harvested by periodical tapping of the trunk bark. Ethylene enhances and prolongs latex flow and latex regeneration. Ethephon, which is an ethylene-releasing compound, applied to the trunk before tapping usually results in a 1.5- to 2-fold increase in latex yield. However, intense mechanical damage to bark tissues by excessive tapping and/or over-stimulation with ethephon induces severe oxidative stress in laticifer cells, which often causes tapping panel dryness (TPD) syndrome. To enhance NR production without causing TPD, an improved understanding of the molecular mechanism of the ethylene response in the Para rubber tree is required. Therefore, we investigated gene expression in response to ethephon treatment using Para rubber tree seedlings as a model system. Results After ethephon treatment, 3270 genes showed significant differences in expression compared with the mock treatment. Genes associated with carotenoids, flavonoids, and abscisic acid biosynthesis were significantly upregulated by ethephon treatment, which might contribute to an increase in latex flow. Genes associated with secondary cell wall formation were downregulated, which might be because of the reduced sugar supply. Given that sucrose is an important molecule for NR production, a trade-off may arise between NR production and cell wall formation for plant growth and for wound healing at the tapping panel. Conclusions Dynamic changes in gene expression occur specifically in response to ethephon treatment. Certain genes identified may potentially contribute to latex production or TPD suppression. These data provide valuable information to understand the mechanism of ethylene stimulation, and will contribute to improved management practices and/or molecular breeding to attain higher yields of latex from Para rubber trees.

Automated summary

Ethephon treatment induces dynamic changes in gene expression in Para rubber tree seedlings, with upregulation of genes associated with carotenoids, flavonoids, and abscisic acid biosynthesis contributing to an increase in latex flow. Downregulation of genes associated with secondary cell wall formation may be due to reduced sugar supply. Understanding the molecular mechanisms of ethylene response in the Para rubber tree can lead to improved latex production practices.