Abstract
N-β-alanyldopamine (NBAD) is a precursor of N-acylquinone sclerotin utilized for cross-linking between cuticular proteins for cuticle during insect molting. The importance of NBAD in cuticle tanning has not been well compared among different developing stages of insects. Henosepilachna vigintioctopunctata, a typical polyphagous pest feeding on a large number of Solanaceae and Cucurbitaceae plants in Asian countries, displays diverse cuticle pigmentation patterns among developing stages and body regions. Here, we found that the expression of three genes (Hvadc, Hvebony, and Hvtan) involved in NBAD biosynthesis peaked in the 4-day-old pupae or 0-day-old adults of H. vigintioctopunctata. At the first, second, third, and fourth larval instar and pupal stage, their transcript levels were high just before and/or right after the molting. Moreover, they were more abundantly transcribed at the larval heads than in the bodies. RNA interference (RNAi) of either Hvadc or Hvebony at the third instar larvae selectively deepened the color of the larval head capsules, antennae, mouthpart, scoli, strumae, and legs; and depletion of the two genes blackened the pupal head capsules, antennae, mouthpart, and legs. However, the knockdown of either Hvadc or Hvebony darkened the whole bodies of the adults. Conversely, RNAi of Hvtan at the third instar stage had little influence on the pigmentation in the larvae, pupae, and adults. These findings demonstrated that Adc and Ebony are important in cuticle pigmentation of H. vigintioctopunctata and suggested that larger quantities of NBAD were present in adults and play more important roles in pigmentation than larvae/pupae.
Highlights
In insects, the cuticle provides protection against physical injury and water loss, rigidness for muscle attachment and mechanical support, and flexibility in intersegmental and joint areas for mobility
The results demonstrate that Adc and Ebony are important in cuticle pigmentation of H. vigintioctopunctata and suggest that larger quantities of NBAD were present in adults and play more important roles in pigmentation than larvae/pupae
The results revealed that Hvadc, Hvebony, and Hvtan were detectable from the embryo to adults
Summary
The cuticle provides protection against physical injury and water loss, rigidness for muscle attachment and mechanical support, and flexibility in intersegmental and joint areas for mobility. Melanization and sclerotization of insect cuticles result from a combination of dark black and brown melanin and light yellow and colorless sclerotins (Wright, 1987; True, 2003; Wittkopp et al, 2003; Wittkopp and Beldade, 2009; Zhan et al, 2010). These melanizing and sclerotized reagents are produced from tyrosine. This reaction is reversible, with the reverse reaction catalyzed by an NBAD hydrolase (Tan). (4) Oxidation of NADA and NBAD to NADA-quinone and NBAD-quinone, which are polymerized to form the corresponding N-acylquinoid sclerotins (Phillips et al, 2005; Simon et al, 2009; Noh et al, 2016; Mun et al, 2020)
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