Isolation and characterization of two distinct classes of DXS genes in Hevea brasiliensis.

Two cDNAs encoding two distinct classes of DXSs were cloned from leaves (HbDXS1) and latex (HbDXS2) of Hevea brasiliensis by RT-PCR based methods. HbDXS1 encodes a protein of 720 amino acids, with a high homology to the class I of plant DXS proteins, and HbDXS2 encodes a protein predicted to contain 711 amino acids and with a high homology to the plant DXS class II proteins. Several important motifs and amino acid positions characteristic of DXS proteins are strictly conserved in both new HbDXS proteins. The two HbDXS genes were differentially expressed in various tissues of H. brasiliensis. The transcriptional levels of HbDXS2 were similar in both a high-yielding rubber clone (RRIM 600) and the wild type. Ethephon increased the latex yield and caused a transient increase of expression of the HbDXS2 gene. The expression of HbDXS2 in latex indicates that it may have a primary function in carotenoid biosynthesis rather than for natural rubber.