Differential antifungal and calcium channel-blocking activity among structurally related plant defensins

A putative novel role for plant defensins: a defensin from the zinc hyper-accumulating plant, Arabidopsis halleri, confers zinc tolerance

The metal tolerance of metal hyper-accumulating plants is a poorly understood mechanism. In order to unravel the molecular basis of zinc (Zn) tolerance in the Zn hyper-accumulating plant Arabidopsis halleri ssp. halleri, we carried out a functional screening of an A. halleri cDNA library in the yeast Saccharomyces cerevisiae to search for genes conferring Zn tolerance to yeast cells. The screening revealed four A. halleri defensin genes (AhPDFs), which induced Zn but not cadmium (Cd) tolerance in yeast. The expression of AhPDF1.1 under the control of the 35S promoter in A. thaliana made the transgenic plants more tolerant to Zn than wild-type plants, but did not change the tolerance to Cd, copper (Cu), cobalt (Co), iron (Fe) or sodium (Na). Thus, AhPDF1.1 is able to confer Zn tolerance both to yeast and plants. In A. halleri, defensins are constitutively accumulated at a higher level in shoots than in A. thaliana. A. halleri defensin pools are Zn-responsive, both at the mRNA and protein levels. In A. thaliana, some but not all defensin genes are induced by ZnCl2 treatment, and these genes are not induced by NaCl treatment. Defensins, found in a very large number of organisms, are known to be involved in the innate immune system but have never been found to play any role in metal physiology. Our results support the proposition that defensins could be involved in Zn tolerance in A. halleri, and that a role for plant defensins in metal physiology should be considered.

Cloning, characterization and antifungal activity of defensin Tfgd1 from Trigonella foenum-graecum L

Defensins are small cysteine rich peptides with a molecular mass of 5-10 kDa and some of them exhibit potent antifungal activity. We have cloned the coding region of a cDNA of 225 bp cysteine rich defensin, named as Tfgd1, from the legume Trigonella foenum-graecum. The amino acid sequence deduced from the coding region comprised 74 amino acids, of which the N-terminal 27 amino acids constituted the signal peptide and the mature peptide comprised 47 amino acids. The protein is characterized by the presence of eight cysteine resisdues, conserved in the various plant defensins forming four disulphide bridges, which stabilize the mature peptide. The recombinant protein expressed in E coli exhibited antifungal activity against the broad host range fungus, Rhizoctonia solani and the peanut leaf spot fungus, Phaeoisariopsis personata.

Characterization of the maize xylem sap proteome

The xylem in plants has mainly been described as a conduit for water and minerals, but emerging evidence also indicates that the xylem contains protein. To study the proteins in xylem sap, we characterized the identity and composition of the maize xylem sap proteome. The composition of the xylem sap proteome in maize revealed proteins related to different phases of xylem differentiation including cell wall metabolism, secondary cell wall synthesis, and programmed cell death. Many proteins were found to be present as multiple isoforms and some of these isoforms are glycosylated. Proteins involved in defense mechanisms were also present in xylem sap and the sap proteins were shown to have antifungal activity in bioassays.

Plant gamma-thionins: novel insights on the mechanism of action of a multi-functional class of defense proteins

This review focuses on the first plant defense protein class described in literature, with growth inhibition activity toward pathogens. These peptides were named gamma-thionins or defensins, which are small proteins that can be classified into four main subtypes according to their specific functions. Gamma-thionins are small cationic peptides with different and special abilities. They are able to inhibit digestive enzymes or act against bacteria and/or fungi. Current research in this area focuses particularly these two last targets, being the natural crop plant defenses improved through the use of transgenic technology. Here, we will compare primary and tertiary structures of gamma-thionins and also will analyze their similarities to scorpion toxins and insect defensins. This last comparison offers some hypothesis for gamma-thionins mechanisms of action against certain pathogens. This specific area has benefited from the recent determination of many gamma-thionin structures. Furthermore, we also summarize molecular interactions between plant gamma-thionins and fungi receptors, which include membrane proteins and lipids, shedding some light over pathogen resistance. Researches on gamma-thionins targets could help on plant genetic improvement for production of increased resistance toward pathogens. Thus, positive results recently obtained for transgenic plants and future prospects in the area are also approached. Finally, gamma-thionins activity has also been studied for future drug development, capable of inhibit tumor cell growth in human beings.

Defensin gene family in Medicago truncatula: structure, expression and induction by signal molecules

A large gene family encoding the putative cysteine-rich defensins was discovered in Medicago truncatula. Sixteen members of the family were identified by screening a cloned seed defensin from M. sativa (Gao et al. 2000) against the Institute for Genomic Research's (TIGR) M. truncatula gene index (MtGI version 7). Based on the comparison of their amino acid sequences, M. truncatula defensins fell arbitrarily into three classes displaying extensive sequence divergence outside of the eight canonical cysteine residues. The presence of Class II defensins is reported for the first time in a legume plant. In silico as well as Northern blot and RT-PCR analyses indicated these genes were expressed in a variety of tissues including leaves, flowers, developing pods, mature seed and roots. The expression of these genes was differentially induced in response to a variety of biotic and abiotic stimuli. For the first time, a defensin gene (TC77480) was shown to be induced in roots in response to infection by the mycorrhizal fungus, Glomus versiforme. Northern blot analysis indicated that the tissue-specific expression patterns of the cloned Def1 and Def2 genes differed substantially between M. truncatula and M. sativa. Furthermore, the induction profiles of the Def1 and Def2 genes in response to the signaling molecules methyl jasmonate, ethylene and salicylic acid differed markedly between these two legumes.