Transcript profiles of two wheat lipid transfer protein-encoding genes are altered during attack by Hessian fly larvae

A sequence encoding a putative type-1 lipid transfer protein from wheat (Triticum aestivum L. em Thell) was identified through ‘GeneCalling’, an mRNA profiling technology. The mRNA for the Hfr-LTP (Hessian fly-responsive lipid transfer protein) gene decreased in abundance (196-fold) in susceptible wheat plants over the first eight days of attack by virulent Hessian fly larvae (Mayetiola destructor Say). Hfr-LTP encodes a putative protein containing eight cysteine residues that are conserved among plant LTPs and are responsible for correct protein folding through formation of disulfide bridges. Twelve hydrophobic amino acids in addition to arginine, glycine, proline, serine, threonine and tyrosine, plus an LTP signature sequence were present in conserved positions. A highly conserved signal peptide sequence was also present. Although attack by one virulent larva was sufficient to cause a decrease in Hfr-LTP mRNA abundance, higher infestation levels led to near silencing of the gene. Hfr-LTP transcript levels were not affected by other biotic factors (feeding by bird cherry-oat aphid, Rhopalosiphum padi L., and fall armyworm larvae, Spodoptera frugiperda Smith) or abiotic factors tested (mechanical wounding or treatment with abscisic acid, methyl jasmonate, or salicylic acid). Comparison to a previously described Hessian fly-responsive wheat LTP gene, TaLTP3, confirmed an initial increase in TaLTP3 mRNA in resistant plants. However, when quantified through eight days after egg hatch, responsiveness to infestation level and a marked decrease in susceptible plant TaLTP3 mRNA abundance were detected, as was seen for Hfr-LTP. Possible functions of LTP gene products in wheat–Hessian fly interactions are discussed.