Inhibitory Effects of Plant Trypsin Inhibitors Msti-94 and Msti-16 on Therioaphis trifolii (Monell) (Homoptera: Aphididae) in Alfalfa

The spotted alfalfa aphid (<i>Therioaphis trifolii</i> (Monell)) is a known destructive pest that can significantly reduce alfalfa yields. Two differentially up-regulated alfalfa trypsin inhibitors &#8216;<i>Msti-94</i>&#8217; and &#8216;<i>Msti-16</i>&#8217; in transcriptome were verified in terms of their mRNA levels using RT-qPCR. The prokaryotic expression vector was constructed and its biological functions, including phenotypic and physiological responses, were verified through feeding spotted alfalfa aphids with active recombinant protein mixed with an artificial diet. Gene clone and gene prokaryotic expression confirmed that <i>Msti-94</i> had a size of 651 bp, encoded 216 amino acids with a predicted protein weight of 23.5 kDa, and a pI value of 6.91. Similarly, the size of <i>Msti-16</i> was 612 bp, encoded 203 amino acids, and had a predicted protein weight of 22.2 kDa with a pI value of 9.06. We concluded that both <i>Msti-94</i> and <i>Msti-16</i> acted as a stomach poison with survival rates reduced to 21.7% and 18.3%, respectively, as compared to the control, where the survival rate was significantly (<i>p</i> &lt; 0.05) higher (60.0%). Aphid reproduction rates were significantly reduced, after 72 h of feeding, in both the <i>Msti-94</i> and <i>Msti-16</i> treatments compared to the controls. A concentration of 800 &#956;g/mL (0.8 mg/mL) of recombinant protein and 5000 &#956;g/mL (5 mg/mL) of recombinant expressing bacteria that inhibits the total protease, which ultimately disrupted the activity of trypsin, chymotrypsin, and aminopeptidase.

Abstract licence: CC BY

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