Abstract
Rubber elongation factor (REF) and small rubber particle protein (SRPP) are two key factors for natural rubber biosynthesis. To further understand the roles of these proteins in rubber formation, six different genes for latex abundant REF or SRPP proteins, including REF138,175,258 and SRPP117,204,243, were characterized from Hevea brasiliensis Reyan (RY) 7-33-97. Sequence analysis showed that REFs have a variable and long N-terminal, whereas SRPPs have a variable and long C-terminal beyond the REF domain, and REF258 has a β subunit of ATPase in its N-terminal. Through two-dimensional electrophoresis (2-DE), each REF/SRPP protein was separated into multiple protein spots on 2-DE gels, indicating they have multiple protein species. The abundance of REF/SRPP proteins was compared between ethylene and control treatments or among rubber tree clones with different levels of latex productivity by analyzing 2-DE gels. The total abundance of each REF/SRPP protein decreased or changed a little upon ethylene stimulation, whereas the abundance of multiple protein species of the same REF/SRPP changed diversely. Among the three rubber tree clones, the abundance of the protein species also differed significantly. Especially, two protein species of REF175 or REF258 were ethylene-responsive only in the high latex productivity clone RY 8-79 instead of in RY 7-33-97 and PR 107. Some individual protein species were positively related to ethylene stimulation and latex productivity. These results suggested that the specific protein species could be more important than others for rubber production and post-translational modifications might play important roles in rubber biosynthesis.
Highlights
2500 plants generate natural rubber latex, but Hevea brasiliensis is the only widely used rubber tree for natural latex production [1]
The sequences of the six Rubber elongation factor (REF)/small rubber particle protein (SRPP) genes were confirmed in H. brasiliensis by cDNA clone, and named as REF138, REF175, REF258, and SRPP117, SRPP204, SRPP243 based on their protein length
We proposed specific protein species which are dominant in high latex productivity rubber tree and positive response to ethylene stimulation might be important for natural rubber biosynthesis
Summary
2500 plants generate natural rubber latex, but Hevea brasiliensis is the only widely used rubber tree for natural latex production [1]. Natural rubber biosynthesis is synthesized in the specialized cells which have a cytoplasm called latex [2]. Natural rubber polymer is found in rubber particles enclosed by a contiguous, monolayer biomembrane in the laticifer cells [5,6]. Rubber biosynthesis includes three major processes: the synthesis of the rubber monomer isopentenyl pyrophosphate (IPP); the synthesis of initiator molecules such as geranyl pyrophosphate, farnesyl pyrophosphate, and geranylgeranyl pyrophosphate (APPs); and the elongation of isoprene polymers. The elongation of these subunits into rubber in latex-producing plants occurs at the surface of the rubber particles and is catalyzed by many protein complexes [8,9]. An experiment incubating the extracted rubber particles with [1-14C]-IPP confirmed the production of rubber polymer from IPP by the particles [5,9,10]
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