Cloning and Expression Analysis of HbLEA3, a Gene Associated with Leaf Senescence in Hevea brasiliensis

To uncover the sequence characteristics and transcriptional regulation pattern of a senescence-associated gene HbLEA3, its 652-bp cDNA(including a single ORF of 303-bp, 173-bp 5' UTR, and 176-bp 3' UTR) was isolated from senescing leaves of Hevea brasiliensis by using RT−PCR. The findings indicated that this gene was predicted to encode a polypeptide of 100 amino acids with a calculated molecular weight of 11.61 kDa and isolectric point of 9.07. Composed of a hydrophobic N-terminal and a hydrophilic C-terminal with a grand average of hydrophilicity of −0.498, the protein is predicted to contain a conserved LEA_3 domain and a transit peptide for mitochondrial localization. Homologous analysis revealed that HbLEA3 shares a similarity of more than 60% with homologs in Manihot esculenta, Manihot esculenta, Jatropha curcas, and Theobroma cacao, and its closest homolog in Arabidopsis thaliana or Oryza sativa is AtLEA3(36.0%) and OsLEA10(41.1%), respectively. Expression analysis showed that HbLEA3 is mainly expressed in leaves with a steadily increasing pattern during leaf development except for a transient decline in early-senescing leaves. Moreover, its transcript level appeared to be regulated by various abiotic stresses and plant growth regulators, including cold, PEG, NaCl, H₂O₂, ABA, ethephon, MeJA, and SA. Taken together, our results suggest a key role of HbLEA3 in hormone and abiotic stress responses as well as leaf development.