| Summary: | Histone post-translational modifications (PTMs) represent a key mechanism in the thermal adaptation of the honeybee <i>Apis mellifera</i>. In this study, a chromatin immunoprecipitation assay and qPCR were employed to explore the changes in the methylation states of H3K4m2, H3K4m3, H3K27m2 and H3K27m3 associated with <i>l2efl</i> (ID: 72474, 724405, 724488), histone methyltransferases (HMTs) ((<i>trx</i>) and <i>PR-set7</i>) and Polycomb (<i>Pc</i>) and (<i>Su</i>(<i>z</i>)<i>12</i>) genes in <i>A. m. jemenitica</i> (tolerant subspecies) and <i>A. m. carnica</i> (susceptible subspecies) in response to heat treatment (42 °C for 1 h). The results revealed significant enrichment fold changes in the methylation/demethylation of most H3K4 and H3K27 marks at all targeted genes. These changes increased the profusion of <i>l2efl</i> (ID: 72474, 724405, 724488), histone methyltransferases (HMTs) (<i>trx)</i> and Polycomb (<i>Pc</i>) and <i>Su(z)12</i> and decreased the profusion of HMT (<i>PR-set7</i>) in both honeybee subspecies. The changes in the methylation enrichment folds of histone methyltransferases (HMTs) ((<i>trx), PR-set)</i> and Polycomb (<i>Pc</i>), <i>Su(z)12</i> genes demonstrate the well-harmonized coordination of epigenetic gene regulation in response to heat treatment. Compared to the control, the changes in the methylation enrichment folds of H3K4m3 at Polycomb <i>Su(z)12</i> were about 30× and 100× higher in treated <i>A. m. jemenitica</i> and <i>A.m. carnica,</i> respectively. Similarly, changes in the methylation/demethylation enrichment folds of HMT (<i>trx)</i> and Polycomb (<i>Pc</i>) and <i>Su(z)12</i> were 2–3× higher in <i>A. m. carnica</i> than in <i>A. m. jemenitica</i> after treatment (42 °C). It is evident that post-translational chromatin modification in both honeybee subspecies can diminish heat stress impact by (I) increasing the transcriptional provision of <i>l2efl</i> associated with survival and (II) increasing the silencing of genes associated with general cellular activities.
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