Transcription Analysis of the Beta-Glucosidase Precursor in Wild-Type and l- 4 i Mutant Bombyx mori (Lepidoptera: Bombycidae)

Lethal fourth-instar larvae ( l- 4 i ) mutant of Bombyx mori , a recently discovered novel mutant, die from energy depletion due to genetic mutation. Beta-glucosidase is a common digestive enzyme that hydrolyzes cellulose in the diet to provide energy. In this study, the mRNA expression profiles of B. mori beta-glucosidase precursor ( BmpreBG ) were characterized by reverse transcription polymerase chain reaction and quantitative real-time polymerase chain reaction. The transcription level of BmpreBG varied in different tissues and developmental stages, except in the pupa and moth, which are the no-diet period. Remarkably, the mRNA expression level of BmpreBG was sharply reduced in l- 4 i but not in the wild type, which suggested that the digestive function of the mutant was severely damaged. This was consistent with the l- 4 i phenotypic traits of not eating mulberries, lack of energy, and ultimate death. 5′-rapid amplification of cDNA ends showed, for the first time, that BmpreBG has a 160-bp 5′-untranslated region. These findings suggested that B. mori β-glucosidase precursor was involved in the death process of l- 4 i mutant larvae.