Proteomics Provides Insight into the Interaction between Mulberry and Silkworm

Mulberry leaves have
been selected as a food source for the silkworm
(Bombyx mori) for over 5000 years. However, the interaction
mechanisms of mulberry–silkworm remain largely unknown. We
explore the interaction between mulberry and silkworm at the protein
level. Total proteins were extracted from mulberry leaves and silkworm
feces on day 5 of the fifth larval instar and analyzed on shotgun
liquid chromatography–tandem mass spectrometry, respectively.
In total, 2076 and 210 foliar proteins were identified from mulberry
leaves and silkworm feces, respectively. These proteins were classified
into four categories according to their subcellular location: chloroplast
proteins, mitochondrial proteins, secretory-pathway proteins, and
proteins of other locations. Chloroplast proteins accounted for 68.3%
in mulberry leaves but only 23.2% in the feces. In contrast, secretory-pathway
proteins had low abundance in mulberry leaves (7.3%) but were greatly
enriched to the largest component in the feces (60.1%). Most of the
foliar secretory-pathway proteins in the feces were found to be resistant
to silkworm feeding by becoming involved in primary metabolite, proteinase
inhibition, cell-wall remodeling, redox regulation, and pathogen-resistant
processes. On the contrary, only six defensive proteins were identified
in the fecal chloroplast proteins including two key proteins responsible
for synthesizing jasmonic acid, although chloroplast proteins were
the second largest component in the feces. Collectively, the comparative
proteomics analyses indicate that mulberry leaves not only provide
amino acids to the silkworm but also display defense against silkworm
feeding, although the silkworm grows very well by feeding on mulberry
leaves, which provides new insights into the interactions between
host-plant and insect herbivores.