Molecular Identification and Characterization of a Gene Associated with the Onset of Tapping Panel Dryness (TPD) Syndrome in Rubber Tree (Hevea brasiliensis Muell.) by mRNA Differential Display

Abstract

In rubber tree (Hevea brasiliensis), tapping panel dryness (TPD) syndrome is considered as a complex physiological disorder which affects latex biosynthesis. To identify differentially expressed genes between healthy and TPD-affected trees, mRNA differential display reverse transcriptase polymerase chain reaction (DDRT-PCR) analysis was performed. We isolated 10 differentially expressed cDNA fragments of which one cDNA encoding a putative TOM20 like protein was identified. The cDNA (1,024 bp), corresponding to the HbTOM20 gene (H evea b rasiliensis Translocase of the Outer Mitochondrial Membrane), contained an open reading frame to code for 202 amino acid protein with a theoretical pI value of 9.5 and the calculated protein M (W) was 23.5 kDa. The predicted amino acid sequence contained conserved domains of TOM20 like proteins in the N-terminal. The protein HbTOM20 has 32% and 27% similarity to Populus TOM20 and Solanum TOM20, respectively. Both semi-quantitative RT-PCR and Northern blot results revealed that the HbTOM20 expression was significantly down-regulated in TPD-affected trees compared to healthy one. Accumulation of HbTOM20 mRNA transcripts was significantly higher in the bark tissues collected from healthy region than that of partially affected by TPD (partially dried) while barely detectable in completely TPD-affected area. Differential expression pattern was noticed in three rubber clones representing various degrees of TPD tolerance. These results suggest that down-regulation of HbTOM20 in TPD-affected trees may play an important role in alteration of mitochondrial metabolism resulting in impaired latex biosynthesis.