Abstract
Ethylene is commonly used as a latex stimulant of Hevea brasiliensis by application of ethephon (chloro-2-ethylphosphonic acid); however, the molecular mechanism by which ethylene increases latex production is not clear. To better understand the effects of ethylene stimulation on the laticiferous cells of rubber trees, a latex expressed sequence tag (EST)-based complementary DNA microarray containing 2,973 unique genes (probes) was first developed and used to analyze the gene expression changes in the latex of the mature virgin rubber trees after ethephon treatment at three different time-points: 8, 24 and 48 h. Transcript levels of 163 genes were significantly altered with fold-change values ≥ 2 or ≤ –2 (q-value < 0.05) in ethephon-treated rubber trees compared with control trees. Of the 163 genes, 92 were up-regulated and 71 down-regulated. The microarray results were further confirmed using real-time quantitative reverse transcript-PCR for 20 selected genes. The 163 ethylene-responsive genes were involved in several biological processes including organic substance metabolism, cellular metabolism, primary metabolism, biosynthetic process, cellular response to stimulus and stress. The presented data suggest that the laticifer water circulation, production and scavenging of reactive oxygen species, sugar metabolism, and assembly and depolymerization of the latex actin cytoskeleton might play important roles in ethylene-induced increase of latex production. The results may provide useful insights into understanding the molecular mechanism underlying the effect of ethylene on latex metabolism of H. brasiliensis.
Highlights
Hevea brasiliensis is so far recognized as the only species producing commercially viable quantities of high-quality natural rubber (NR) [1], i.e. cis-1, 4-polyisoprene [2]
Significant increases in the latex yield and the duration of latex flow were observed from unexploited rubber trees stimulated with ethephon for 24 h (Fig 1a and 1b), and remarkable decreases in the plugging index and the total solid content (TSC) were detected from unexploited rubber trees treated with ethephon after 24 h and 48 h (Fig 1c and 1d)
The L2343 encoding pyruvate dehydrogenase that catalyzes the pivotal irreversible reaction of glucose metabolism in the aerobic energy-generating pathways [83] was up-regulated in ethephon-treated rubber trees. These results indicate that the ET stimulation of latex production was associated with accelerating the importation and metabolism of sugar, especially sucrose which improves the supply of carbon and energy (e.g. ATP) for rubber biosynthesis in laticifers of rubber trees
Summary
Hevea brasiliensis (para rubber tree) is so far recognized as the only species producing commercially viable quantities of high-quality natural rubber (NR) [1], i.e. cis-1, 4-polyisoprene [2]. The rubber biosynthesis of rubber trees uses the basic precursor of sucrose in the laticifer’s latex in a typical isoprenoid secondary metabolism [7], which is similar to the isoprenoid biosynthesis of other plant species using IPP as the precursor [8] Many latexexpressed genes, such as HMGR (3-hydroxy-3-methylglutaryl-coenzyme A reductase), farnesyl diphosphate synthase, geranylgeranyl diphosphate synthase (GGPS), rubber elongation factor (REF), small rubber particle protein (SRPP) and cis-prenyltransferase (CPT) participate in the latex regeneration and rubber biosynthesis [9,10,11,12,13,14,15,16]; the gene expression profile and its kinetic change in H. brasiliensis laticifers is very important for investigating the related molecular events of latex metabolism and rubber biosynthesis [17]
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