Thanatin(S) is an analog of thanatin, an insect antimicrobial peptide possessing strong and broad spectrum of antimicrobial
activity. In order to investigate if the thanatin could be used in engineering transgenic plants for increased
resistance against phytopathogens, the synthetic thanatin(S) was introduced into Arabidopsis thaliana
plants. To increase the expression level of thanatin(S) in plants, the coding sequence was optimized by
plant-preference codon. To avoid cellular protease degradation, signal peptide of rice Cht1 was fused to N terminal
of thanatin(S) for secreting the expressed thanatin(S) into intercellular spaces. To evaluate the application value of
thanatin(S) in plant disease control, the synthesized coding sequence of Cht1 signal peptide (Cht1SP)-thanatin(S)
was ligated to plant gateway destination binary vectors pGWB11 (with FLAG tag). Meanwhile, in order to observe
the subcellular localization of Cht1SP-thanatin(S)-GFP and thanatin(S)-GFP, the sequences of Cht1SP-thanatin(S)
and thanatin(S) were respectively linked to pGWB5 (with GFP tag). The constructs were transformed into
Arabidopsis ecotype Col-0 and mutant pad4-1 via Agrobacterium-mediated transformation. The transformants
with Cht1SP-thanatin(S)-FLAG fusion gene were analyzed by genomic PCR, real-time PCR, and western blots and
the transgenic Arabidopsis plants introduced respectively Cht1SP-thanatin(S)-GFP and thanatin(S)-GFP were observed
by confocal microscopy. Transgenic plants expressing Cht1SP-thanatin(S)-FLAG fusion protein showed antifungal
activity against Botrytis cinerea and powdery mildew, as well as antibacterial activity against Pseudomonas
syringae pv. tomato. And the results from confocal observation showed that the GFP signal from Cht1SPthanatin(
S)-GFP transgenic Arabidopsis plants occurred mainly in intercellular space, while that from
thanatin(S)-GFP transgenic plants was mainly detected in the cytoplasm and that from empty vector transgenic
plants was distributed uniformly throughout the cell, demonstrating that Cht1 signal peptide functioned. In addition,
thanatin(S) and thanatin(S)-FLAG chemically synthesized have both in vitro antimicrobial activities against
P. syringae pv. tomato and B. cinerea. So, thanatin(S) is an ideal candidate AMPs for the construction of transgenic
crops endowed with a broad-spectrum resistance to phytopathogens and the strategy is feasible to link a signal peptide
to the target gene.