Plant antimicrobial peptides: an overview of SuperSAGE transcriptional profile and a functional review

Defensin, thionin and lipid transfer protein (LTP) gene families, which antimicrobial activity has an attractive use in protein engineering and transgenic production of agronomical important plants, have been here functionally reviewed. Also, a transcriptional overview of a set of plant SuperSAGE libraries and analysis looking for 26 bp tags possibly annotated for those families is presented. Tags differentially expressed (p = 0.05) or constitutively transcribed were identified from leaves or roots SuperSAGE libraries from important Brazilian plant species [cowpea (Vigna unguiculata (L.) Walp.), soybean (Glycine max (L.) Merr.) and modern sugarcane hybrids (Saccharum spp.)] submitted to abiotic [salt (100 mM NaCl) or drought] or biotic stresses [fungus inoculation (Phakopsora pachyrhizi; Asiatic Soyben Rust phytopathogen)]. The diverse transcriptional patterns observed, probably related to the variable range of targets and functions involved, could be the first step to unravel the antimicrobial peptide world and the plant stress response relationship. Moreover, SuperSAGE opens the opportunity to find some SNPs or even rare transcript that could be important on plant stress resistance mechanisms. Putative defensin or LTP identified by SuperSAGE following a specific plant treatment or physiological condition could be useful for future use in genetic improvement of plants.

Cloning and quantitative expression analysis of drought-induced genes in soybean

We determined the expression levels of DREB transcription factor (Gmdreb1) and of the genes Gmgols, Gmpip1b, Gmereb, and Gmdefensin in drought-tolerant (MG/BR46-Conquista) and drought-sensitive (BR16) genotypes of soybean, during drought. The trial was carried out in a controlled-environment chamber, set up to provide drought conditions. Sequences of Arabidopsis thaliana DREB-family proteins were used to build a phylogenetic tree through the alignment of the conserved regions near the AP2 domain. We found that Gmdreb1 is similar to Atrap2.1, which is located near the AtDREB1 and AtDREB2 families. The amplified fragment was cloned and sequenced; alignment with the sequence available at Genbank showed total similarity. Expression analysis showed that under drought: a) Gmdreb1 expression increased in leaves and roots of both genotypes and expression level changes occurred that were correlated with the length of the water-deficit period; b) there were increased expression levels of Gmdefensin in roots of MG/BR46; c) expression of Gmgols increased in leaves and roots of the two genotypes; d) Gmpip1b expression generally increased, except in roots of BR16, and e) the same was found for Gmereb, except in roots of MG/BR46.

Size of AT(n) insertions in promoter region modulates Gmhsp17.6-L mRNA transcript levels

During earlier experiments, an SSR molecular marker (176 Soy HSP) showing high correlation (70%) with resistance/susceptibility to javanese root-knot nematode Meloidogyne javanica was identified in soybean. After being sequenced, results indicated that the SSR 176 Soy HSP marker was inserted in the promoter region of Gmhsp17.6-L gene. It was also detected in this region that resistant genotypes presented insertions between AT(31) and AT(33) in size and susceptible genotypes, AT(9). Gmhsp17.6-L gene coding region presented a perfect match in amino acid sequence in all soybean genotypes. A ribonuclease protection assay showed that Gmhsp17.6-L gene mRNA transcripts were present in all genotypes. A real-time relative quantification (qPCR) indicated in the resistant individuals higher mRNA transcripts levels, which presented in the sequencing more AT(n) insertions. These results suggest that the number of AT(n) insertions inside this promoter region could modulate up or down gene levels. Those findings can lead to the possibility of manipulating, between some limits, the mRNA transcripts levels using different sizes of AT(n) insertions.