Physiological and Proteomic Analyses of Molybdenum- and Ethylene-Responsive Mechanisms in Rubber Latex

Abstract

Molybdenum (Mo) is an essential micronutrient in many plants. In the rubber tree Hevea brasiliensis, Mo application can reduce the shrinkage of the tapping line, decrease tapping panel dryness, and finally increase rubber latex yield. After combined Mo with ethylene (Eth), these effects become more obvious. However, the molecular mechanism remains unclear. Here, we compared the changed patterns of physiological parameters and protein accumulation in rubber latex after treated with Mo and/or Eth. Our results demonstrated that both Eth and Mo can improve the contents of thiol, sucrose, and dry yield in rubber latex. However, lutoid bursting is significantly inhibited by Mo. Comparative proteomics identified 169 differentially expressed proteins, including 114 unique proteins, which are mainly involved in posttranslational modification, carbohydrate metabolism, and energy production. The abundances of several proteins involved in rubber particle aggregation are decreased upon Mo stimulation, while many enzymes related to natural rubber biosynthesis are increased. Comparison of the accumulation patterns of 25 proteins revealed that a large portion of proteins have different changed patterns with their gene expression levels. Activity assays of six enzymes revealed that Mo stimulation can increase latex yield by improving the activity of some Mo-responsive enzymes. These results not only deepen our understanding of the rubber latex proteome but also provide new insights into the molecular mechanism of Mo-stimulated rubber latex yield.

Identification and Characterization of Glycoproteins and Their Responsive Patterns upon Ethylene Stimulation in the Rubber Latex

“…Fructokinase is a kinase that catalyzes the transfer of phosphate groups to fructose and can phosphorylate the sugar at the C-1 position, and thus is considered as one of the rate-limiting enzymes of glycolysis [ 54 ]. Recent rubber latex proteomics data revealed that fructokinase can be induced by ethylene treatment [ 55 ], but in this study, we found this enzyme can be glycosylated and its abundance was decreased after ethylene stimulation for five days ( Table S2 ). Aldehyde dehydrogenase is a kind of oxidizing enzyme that is involved in detoxification of both exogenous and endogenous aldehyde substrates through NAD(P) + -dependent oxidation.…”

“…Its gene expression was up-regulated in the latex of a tapping panel dryness [ 57 ] and a high-yielding rubber tree [ 54 ]. Proteomics analyses revealed that this protein is highly abundant in the washed solutions of rubber particles [ 48 ] and was significantly induced in rubber latex after ethylene application [ 55 ]. Another enzyme, glutamine synthetase, plays an important role in metabolizing nitrogen by catalyzing the reaction of condensation of glutamate and ammonia to form glutamine, and the glutamine–glutamate synthase cycle might be the major pathway for the amino acid and protein synthesis required for natural latex regeneration [ 4 ].…”

“…Among them, three ACAT isoforms were detected from spots 68, 71 and 97, respectively ( Figure 7 ). These protein isoforms may generate by alternative splicing and different kinds of post-translational modifications [ 55 ]. Three ACAT genes were determined in the rubber tree genome [ 63 ].…”

Effectiveness of commercially available selected water-based and oil-based ethephon formulations as a yield stimulant of rubber (<em>Hevea brasiliensis</em>)

“…These systems allow trees to be tapped in a lesser frequency or lesser amount of bark consumption and ensure sustained production in rubber plantations (Njukeng et al, 2011). Ethephon is used as the yield stimulant along with the LIH systems in order to recover the yield loss due to the reduction of harvesting intensity (Gao et al, 2018). Ethephon is a kind of plant growth regulator that penetrates into the plant tissues and decomposes to produce ethylene that increases activities of anabolic physiological processes such as biosynthesis of rubber and related proteins (Tseng et al, 2000;Coupe and Chrestin, 1989).…”

“…Furthermore, effect of ethephon on cell membrane permeability results in decrease of laticiferous vessel obstruction (Zhu and Zhang, 2009). As a result of delaying the plugging of latex vessels, the duration of latex flow is increased (Emuedo et al, 2017;Gao et al, 2018). Thereby the yield per tapping is increased (Kudaligama et al, 2013).…”