ARS | Publication request: Functional specialization among insect chitinase family genes revealed by RNA interference

Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 6, 2008
Publication Date: May 6, 2008
Citation: Zhu, Q., Arakane, Y., Beeman, R.W., Kramer, K.J., Muthukrishnan, S. 2008. Functional specialization among insect chitinase family genes revealed by RNA interference. Proceedings of the National Academy of Sciences 105: 6650-6655.

Interpretive Summary: The red flour beetle recently became the first agricultural pest insect to have all 16,000 of its genes identified. This achievement creates a valuable resource for pest biology, namely a large number of new genes that could be studied to understand pest survival strategies, and that could be exploited as biopesticide targets. We examined the functions of a set of “chitinase-like” genes thought to be involved in recycling of the exoskeleton. Each gene was inactivated by a technique called “RNA interference”, and the effect on the insect was observed. We found that many of the chitinase genes are essential for life, but that each one has a different function. For example, some are required only for the adult exoskeleton while others are needed for the larval exoskeleton. These findings add to the list of vital insect genes that might be targeted for disruption for pest control purposes.

Technical Abstract: The biological functions of individual members of the large family of chitinase-like proteins from the red flour beetle, Tribolium castaneum, were examined using gene-specific RNA interference (RNAi). One chitinase, TcCHT5, was found to be required for pupal-adult molting only. A lethal phenotype was observed when the transcript level of TcCHT5 was down-regulated by injection of TcCHT5-specific, double-stranded RNA (dsRNA) into larvae. The larvae had metamorphosed into pupae and then to pharate adults but did not complete adult eclosion. Specific knockdown of transcripts for another chitinase, TcCHT10 that has multiple catalytic domains, prevented embryo hatch, larval molting, pupation and adult metamorphosis, indicating a vital role for TcCHT10 during each of these processes. A third chitinase-like protein, TcCHT7, was required for abdominal contraction and wing/elytra extension immediately after pupation, but was dispensable for larval-larval molting, pupation and adult eclosion. The wing/elytra abnormalities found in TcCHT7-silenced pupae were also manifest in the ensuing adults. A fourth chitinase-like protein, TcIDGF4, exhibited no chitinolytic activity but contributed to adult eclosion. No phenotypic effects were observed after knockdown of transcripts for several other chitinase-like proteins including IDGF2. These data indicate functional specialization among insect chitinase family genes, primarily during the molting process, and provide a biological rationale for the presence of a large assortment of chitinase-like proteins.