Molecular cloning and characterization of a thaumatin-like protein-encoding cDNA from rough lemon

Plants accumulate defense-related proteins when they suffer attacks by fungi and bacteria, diverse stress conditions, or elicitor treatment. Among the defense-related proteins, thaumatin-like proteins (TLPs) are well known to function as anti-fungal proteins. A full-length cDNA from rough lemon (Citrus jambhiri Lush.) that encodes a thaumatin-like protein was cloned by RACE and designated RlemTLP. Transcripts of RlemTLP were not detected in leaves, stems, and roots, but were accumulated in leaves after wounding treatment. RlemTLP transcripts were also accumulated in leaves after fungal inoculation or jasmonic acid treatment. RlemTLP protein obtained by using an Escherichia coli expression system produced anti-fungal activity to Alternaria alternata. Subcellular localization analysis showed that GFP-tagged RlemTLP was predominantly localized to both the periphery of the plasma membrane and the cytoplasm. These results suggested that RlemTLP is likely to be involved in the defense of rough lemon against fungal pathogens.