Abstract
A large percentage of crop loss is due to insect damage, especially caterpillar damage. Plant chitinases are considered excellent candidates to combat these insects since they can degrade chitin in peritrophic matrix (PM), an important protective structure in caterpillar midgut. Compared to chemical insecticides, chitinases could improve host plant resistance and be both economically and environmentally advantageous. The focus of this research was to find chitinase candidates that could improve plant resistance by effectively limiting caterpillar damage. Five classes of endochitinase (I-V) genes were characterized in the maize genome, and we isolated and cloned four chitinase genes (chitinase A, chitinase B, chitinase I, and PRm3) present in two maize (Zea mays L.) inbred lines Mp708 and Tx601, with different levels of resistance to caterpillar pests. We also investigated the expression of these maize chitinases in response to fall armyworm (Spodoptera frugiperda, FAW) attack. The results indicated that both chitinase transcript abundance and enzymatic activity increased in response to FAW feeding and mechanical wounding. Furthermore, chitinases retained activity inside the caterpillar midgut and enzymatic activity was detected in the food bolus and frass. When examined under scanning electron microscopy, PMs from Tx601-fed caterpillars showed structural damage when compared to diet controls. Analysis of chitinase transcript abundance after caterpillar feeding and proteomic analysis of maize leaf trichomes in the two inbreds implicated chitinase PRm3 found in Tx601 as a potential insecticidal protein.
Highlights
IntroductionMaize (Zea mays L.), as one of the most important crops, suffers great damage from a wide range of insect pests especially in tropical regions (McMullen et al 2009), and fall armyworm (Spodoptera frugiperda, FAW) is one of them
Herbivorous insects are one major cause of crop losses worldwide
Chitinase Activity was Detected in Plant-fed FAW Midguts and Frass. We found both chitinase gene expression and activity were up-regulated in maize leaves upon insect damage, it remains debatable if these enzymes would retain activity inside the caterpillar since pH is typically alkaline in the midgut and plant chitinases have been shown to have little or no activity at high pH (Dow 1992; Pegg and Young 1982; Zhe-fu et al 1992)
Summary
Maize (Zea mays L.), as one of the most important crops, suffers great damage from a wide range of insect pests especially in tropical regions (McMullen et al 2009), and fall armyworm (Spodoptera frugiperda, FAW) is one of them. To control this devastating pest, current pest control methods largely rely on chemical insecticides or genetically modified crops (GMOs) (Aranda et al 1996; Bohorova et al 2001; Bokonon-Ganta et al 2003; Huang 2020). More attention should be given to the identification and characterization of endogenous genes that can increase maize resistance against herbivore pests
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