AOBPreview originally published online on October 3, 2007
Annals of Botany 2007 100(6):1199-1208; doi:10.1093/aob/mcm216
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Vegetative Storage Protein in Litchi chinensis, a Subtropical Evergreen Fruit Tree, Possesses Trypsin Inhibitor Activity
1 Key Laboratory of Agriculture Ministry for the Cultivation and Physiology of Tropical Crops, Rubber Research Institute, Chinese Academy of Tropical Agricultural Sciences, Danzhou, Hainan 571737, China
2 National Key Biotechnology Laboratory for Tropical Crops, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China
3 Institute of Botany, Northwest University, Xi'an 710069, China
* For correspondence. E-mail: wmtian1965{at}hotmail.com
Received: 21 February 2007 Returned for revision: 25 April 2007 Accepted: 20 July 2007 Published electronically: 3 October 2007
Background and Aims: Vegetative storage proteins (VSPs) are commonly bioactive in herbaceous plants but few VSPs with bioactivity have been identified in trees. In addition, information on the characterization of VSPs in evergreen trees is limited. The objective of this study was to characterize the VSPs with bioactivity in evergreen trees.
Methods: The VSP in lychee (Litchi chinensis), an evergreen fruit tree, was characterized by a combination of cytological, biochemical and molecular biological techniques.
Key Results: The VSP in lychee was a 22-kDa protein. It accumulated in the large central vacuoles of protein-storing cells (PSCs) in two distinguishable forms, granular and floccular. The PSCs were of a novel type. The 22-kDa protein is distributed in mature leaves, bark tissues of branches, trunk and large roots, paralleling the distribution of PSCs. Its homologues were present in mature seed. During young shoot development and fruiting, the 22-kDa protein decreased apparently, suggesting a nitrogen-storage function. The 22-kDa protein had several isoforms encoded by a small multigene family. One gene member, LcVSP1, was cloned. The LcVSP1 had no intron and contained a 675 bp open reading frame encoding a putative protein of 225 amino acids. LcVSP1 was homologous to Kunitz trypsin inhibitors. The 22-kDa protein inhibited trypsin and chymotrypsin, but had no inhibitory effect on subtilisin.
Conclusions: Lychee is rich in a 22-kDa VSP with trypsin inhibitor activity. The VSP plays an important role in nitrogen storage while its possible defensive function remains to be elucidated.
Key words: Defence, evergreen tree, Kunitz trypsin inhibitor, Litchi chinensis, nitrogen storage, vegetative storage protein