RESUMO
The extensive and indiscriminate use of chemical pesticides in agriculture has led to adverse effects on human health, environmental pollution, and the emergence of pesticide-resistant pests. To mitigate these challenges, the development of environmentally friendly alternatives is crucial, with biopesticides emerging as promising solutions such as peptides. Legume seeds naturally contain diverse insecticidal peptides or proteins to combat pest attacks. One such peptide is PA1b (Pea Albumin 1, subunit b), a 37 amino acid extracted from pea seeds (Pisum sativum). PA1b has shown significant potential in controlling cereal weevils (Sitophilus spp.), a major pest of stored cereals. Here, we screened PA1b-like peptides in five wild seeds of vetches (Vicia sativa subsp. sativa) from the Middle East. Using a comprehensive set of biochemical, biological, and molecular techniques, we characterized different PA1b homologs and assessed their toxicity and expression profiles. Our results reveal that PA1b homolog from Vicia sativa subsp. sativa originating from turkey displays outstanding insecticidal activity against Sitophilus oryzae through binding to the receptor site found in the midgut of the insect. Moreover, it exhibits a strong cytotoxic effect against Sf9 cells. This cysteine-rich peptide shows sequence identity and the same hydrophobic pole as AG41, a tenfold more toxic isoform of PA1b from Medicago truncatula. Such observations pave the way for the development of bioinsecticides, with PA1b-like peptides as lead compounds.
RESUMO
BACKGROUND: Albumin 1b peptides (A1b) are small disulfide-knotted insecticidal peptides produced by Fabaceae (also called Leguminosae). To date, their diversity among this plant family has been essentially investigated through biochemical and PCR-based approaches. The availability of high-quality genomic resources for several fabaceae species, among which the model species Medicago truncatula (Mtr), allowed for a genomic analysis of this protein family aimed at i) deciphering the evolutionary history of A1b proteins and their links with A1b-nodulins that are short non-insecticidal disulfide-bonded peptides involved in root nodule signaling and ii) exploring the functional diversity of A1b for novel bioactive molecules. RESULTS: Investigating the Mtr genome revealed a remarkable expansion, mainly through tandem duplications, of albumin1 (A1) genes, retaining nearly all of the same canonical structure at both gene and protein levels. Phylogenetic analysis revealed that the ancestral molecule was most probably insecticidal giving rise to, among others, A1b-nodulins. Expression meta-analysis revealed that many A1b coding genes are silent and a wide tissue distribution of the A1 transcripts/peptides within plant organs. Evolutionary rate analyses highlighted branches and sites with positive selection signatures, including two sites shown to be critical for insecticidal activity. Seven peptides were chemically synthesized and folded in vitro, then assayed for their biological activity. Among these, AG41 (aka MtrA1013 isoform, encoded by the orphan TA24778 contig.), showed an unexpectedly high insecticidal activity. The study highlights the unique burst of diversity of A1 peptides within the Medicago genus compared to the other taxa for which full-genomes are available: no A1 member in Lotus, or in red clover to date, while only a few are present in chick pea, soybean or pigeon pea genomes. CONCLUSION: The expansion of the A1 family in the Medicago genus is reminiscent of the situation described for another disulfide-rich peptide family, the "Nodule-specific Cysteine-Rich" (NCR), discovered within the same species. The oldest insecticidal A1b toxin was described from the Sophorae, dating the birth of this seed-defense function to more than 58 million years, and making this model of plant/insect toxin/receptor (A1b/insect v-ATPase) one of the oldest known.
