Following pathogen attack in a host, widespread changes are induced in the host's gene expression, in particular those involved in the immune system, growth and survival. Epigenetic mechanisms have been suggested to be involved in the regulation of these changes through a number of mechanisms. DNA methylation is one of the important epigenetic processes that is carried out by DNA (cytosine-5) methyltransferase (DNMT) and alters expression of target genes. Here, we identified two putative sequences of DNMT (i.e. DNMT1 and DNMT2) from the transcriptome dataset of Helicoverpa armigera that showed high similarity to the homologous sequences in Bombyx mori. Domain architectures of DNMT1 and DNMT2 exhibit the unique pattern of DNMTs that highlights conserved function of these genes in different insects. To see if these genes play any role in bacterial infection, we challenged the fifth instar larvae of H. armigera by injecting Bacillus thuringiensis and Serratia marcescens cells into the hemolymph. Transcript levels of the DNMTs were analyzed by RT-qPCR. The results showed that the expression levels of DNMT1 and DNMT2 increased in the bacteria-injected larvae. Injection of the heat-killed bacteria also induced the expression of the DNMTs, but lower than that of the live bacteria. To determine whether these genes function during bacterial infection, we injected the inhibitor of DNMTs, 5-azacytidine (5-AZA), into the larvae and 24 h later, the bacterial cells were also injected into the larvae. Bacterial replication and larval mortality were analyzed in the treated and control insects. We found that 5-AZA reduced bacterial replication and also mortality of the bacterial-injected larvae regardless of the pathogenic bacterial species. Interestingly, the expression levels of antimicrobial peptides (AMPs) were also modulated following 5-AZA treatment. In conclusion, we showed that upregulation of the DNMTs in H. armigera following bacterial infections modulates AMPs and thereby affects the insect-bacteria interactions.

中文翻译：

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注射致病菌后，棉铃虫中DNA甲基转移酶基因的诱导可调节抗菌肽的表达并影响细菌增殖。

病原体侵袭宿主后，宿主的基因表达会发生广泛变化，尤其是那些与免疫系统，生长和存活有关的基因表达。已经提出表观遗传机制通过多种机制参与这些变化的调控。DNA甲基化是DNA（胞嘧啶5）甲基转移酶（DNMT）进行并改变靶基因表达的重要表观遗传过程之一。在这里，我们从棉铃虫的转录组数据集中确定了两个假定的DNMT序列（即DNMT1和DNMT2），它们与家蚕中的同源序列具有高度相似性。DNMT1和DNMT2的域结构展示了DNMT的独特模式，突出了这些基因在不同昆虫中的保守功能。为了查看这些基因是否在细菌感染中起作用，我们通过向血淋巴中注射苏云金芽孢杆菌和粘质沙雷氏菌细胞挑战了棉铃虫的第五龄幼虫。通过RT-qPCR分析DNMT的转录水平。结果表明，在经细菌注射的幼虫中，DNMT1和DNMT2的表达水平增加。注射热灭活细菌也诱导了DNMT的表达，但是低于活细菌。为了确定这些基因在细菌感染期间是否起作用，我们将DNMTs抑制剂5-氮杂胞苷（5-AZA）注入幼虫中，并在24小时后将细菌细胞也注入幼虫中。在治疗和对照昆虫中分析细菌的复制和幼虫的死亡率。我们发现5-AZA减少了细菌复制，也降低了注射细菌的幼虫的死亡率，而与致病细菌种类无关。有趣的是，在5-AZA处理后，还调节了抗菌肽（AMPs）的表达水平。总之，我们表明在细菌感染后，棉铃虫中DNMTs的上调会调节AMPs，从而影响昆虫与细菌的相互作用。