Molecular Cloning and Analysis of HbCAB2, A Chlorophyll a/b-binding Protein-Encoding Gene from Hevea brasiliensis

Based on the in silico cloning result, an 858-bp cDNA that includes a 798-bp long ORF (open reading frame, designated HbCAB2) was isolated from the Hevea brasiliensis leaf by using the RT-PCR technique. Sequence analysis indicated that this gene putatively encodes 265 amino acids with a chloroplast signal peptide of 35 residues, and the mature protein was predicted to have a theoretical molecular weight (Mw) of 24.66 kDa and an isolectric point (pI) of 4.99. HbCAB2 can be categoried into subtype LHCB1, which was shown to contain one conserved light-harvesting chlorophyll a/b binding domain (Chloroa_b-bind, Pfam ID PF00504) as well as 3 transmembrane helices and 2 short helices, 1 trimerization motif, some chlorophyll and carotenoid binding sites. HbCAB2 was shown to be a reverse tandem duplication of HbCAB1, which shares a sequence similarity of 97.0% at the protein level. Expression analysis revealed that HbCAB2 was preferentially expressed in leaves and female flowers, with a gradually increased expression pattern during leaf maturity but a sharply decrease in senescent leaves. Additionally, its transcript level was shown to be inhibited by pathogen infection, low temperature, and drought stresses.