Seasonal variation in expression patterns of anti-microbial peptides and activity of anti-oxidant defence enzymes in muga silkworm larvae, Antheraea assamensis Helfer.

Abstract

Muga is a semi-domesticated multi-voltine silkworm cultivated in different seasons of the year. Crops are reared in specific months and are traditionally named Jarua (spring), Chotua, Bohogua, Jethua, Aherua, Saonia, Bhodia, Ahinia, Katia (autumn) and Aghonia. Seasonal variation forces silkworm larvae to face harsh environmental conditions manifested by generation of oxidative stress and occurrence of microbial diseases. Anti-oxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione-S-transferase (GST) along with anti-microbial peptides like cecropin, gloverin, and defensin in lepidopterans play a significant role in fighting against free radicals as well as disease-causing microbes, and hence this study has focussed on the expression of anti-oxidant enzyme activity and different anti-microbial peptides in three distinct crops, namely, Jarua and Aherua (seed crops) and Katia (commercial crop) collected from the same site, Khanapara (26°09'34.62″N; 91°41'27.23″E) in Assam, India. The results of biochemical enzyme assays revealed the Jarua crop to possess the highest enzyme activity with respect to SOD and GST in particular, followed by the Katia and Aherua crops. Malondialdehyde lipid peroxidase and reduced glutathione were also expressed notably in the Jarua crop. The quantitative polymerase chain reaction (qPCR) study involving analysis of anti-microbial peptide (AMP) expression revealed the Jarua crop to possess the highest expression of three AMPs, viz., gloverin, moricin 1 and gallerimycin pro, followed by Katia with the highest expression of attacin and defensin. Total haemocyte count revealed Jarua to induce the least haemocyte count, Katia to induce moderate, and Aherua to induce the highest count. Thus, our findings indicate that although the Jarua crop is considered a seed crop, it can be reconsidered as a commercial crop due to its high concentration of anti-oxidant enzymes and higher expression of AMPs. This study was carried out to focus on the immunological response of the muga silkworm with varying seasons. Their innate immunity helps them fight against diseases that emerge under different environmental conditions in which anti-microbial peptides play a crucial role. Muga larvae are reared for silk and are used commercially to produce various commodities for which the best silk thread should always be identified to obtain a higher market value.