Genome-wide identification and characterisation of hevein precursor genes in Hevea brasiliensis

Hevea brasiliensis is the primary source of natural rubber, which is obtained from its latex and used in the manufacturing of various products. Hevein is a small protein found in the latex, produced by post-translational cleavage of prohevin, which is encoded by the hevein precursor gene. It exhibits antimicrobial and agglutination properties. Several nucleotide sequences that encode the hevein precursor genes were reported, however, the sequences are not characterised well. In the present study, four full-length hevein precursor sequences (Hevein 1–4) were obtained by manually curating the sequences from different databases. All sequences show high homology with the highest identity between Hevein 1 and Hevein 3. In a phylogenetic analysis along with sequences from related plants, all sequences from H. brasiliensis were clustered into a specific clade. All hevein precursor genes were expressed in the latex samples obtained from three clones; RRIM 600, RRIM 3001 and PB 350 of less than one year old and five-year-old RRIM 3001 plants, grown in plant house, as well as field-grown trees of clone PB 350 belonging to three different ages; two years, six years and fifteen years. All hevein precursor genes in the five-year-old RRIM 3001 plants with stunted growth, maintained in the plant house showed alternative splicing. Hevein 3 was expressed with two splice variants, one with intron retention and the other without intron whereas the other genes were expressed with only intron retained variant. Differential expression analysis using nanoplate digital PCR showed that Hevein 2 and Hevein 3 were expressed with no significant difference among the three young H. brasiliensis clones. The expression of Hevein 2 and Hevein 3 among the H. brasiliensis clone PB 350 of different ages grown in field conditions showed significant difference. The present study provides a better understanding on the importance of hevein precursor genes in different physiological responses which will be useful for further research leading to the genetic improvement of H. brasiliensis.