EXPRESSION OF RUBBER ELONGATION FACTOR (REF) AND SMALL RUBBER PARTICLE PROTEIN (SRPP) RELATES TO DRY RUBBER YIELD OF CLONAL VARIETIES

Abstract

REF and SRPP are necessary for a functional role in rubber polymerization. It involved in the final
polymerization step of natural rubber biosynthesis in Hevea. The aims of this research were to relate the REF and
SRPP gene expressions and latex yield, in order to use these genes as markers in selection criteria of rubber tree
breeding programs. Dry rubber yield and expressions of the two genes were determined for four selected clones
(SK1, SK3, NK1 and T2) and the by location paired controls (RRIM 600 clone). Results from cDNA sequencing
indicated the REF amino acid sequence of lower yield clone present one amino acid, which is different from
Proline (CCC) as Serine at site 113 (CCT). The SRPP amino acid sequences, Glutamic acid are absence at site 6
of RRIM 600. One amino acid at site 67 of RRIM 600 clone was different from other clone resulting in Threonine
(ACT) instead of Alanine (GCT). In NK1 clone, at site 178, different in one protein was recorded different code
protein from Threonine (ACT) to Valine (GTT). The annual dry rubber yields of the four clones exceeded that of
RRIM 600. Quantitative RT-PCR showed a positive relationship between latex yield and expression levels of
REF and SRPP genes. In seedling leaves, REF and SRPP genes were expressed at low level, but both genes were
abundantly expressed in bark. These results suggest good potential in the early selection of rubber trees, in
breeding programs for yield improvement.