Heat Shock Transcriptional Responses in an MC-Producing Cyanobacterium (Planktothrix agardhii) and Its MC-Deficient Mutant under High Light Conditions

Abstract

Microcystins (MCs) are the most commonly-reported hepatotoxins produced by various cyanobacterial taxa in fresh waters to constitute a potential threat to human and animal health. The biological role of MCs in the producer organisms is not known, and it would be very useful to understand the driving force behind the toxin production. Recent studies have suggested that MCs may have a protective function in cells facing environmental stress. Following this starting premise, we speculate that under adverse conditions the expression of stress-related genes coding for Heat Shock Proteins (Hsp) might be different in an MC-producing strain and its MC-deficient mutant. We therefore used RT-qPCR to compare the expression of 13 hsp genes of an MC-producing strain of Planktothrix agardhii (CYA126/8) and its MC-deficient ΔmcyD mutant over different periods of exposure to high light stress (HL). Three reference genes (RGs) were selected from six candidates to normalize the RT-qPCR data. Of these three RGs (rsh, rpoD, and gltA), gltA is used here for the first time as an RG in prokaryotes. Under HL stress, five genes were found to be strongly up-regulated in both strains (htpG, dnaK, hspA, groES, and groEL). Unexpectedly, we found that the MC-producing wild type strain accumulated higher levels of htpG and dnaK transcripts in response to HL stress than the MC-deficient mutant. In addition, a significant increase in the mcyE transcript was detected in the mutant, suggesting that MCs are required under HL conditions. We discuss several possible roles of MCs in the response to HL stress through their possible involvement in the protective mechanisms of the cells.

Influence of temperature, mixing, and addition of microcystin-LR on microcystin gene expression inMicrocystis aeruginosa

“…S4). This is in agreement with other studies that assessed this gene as a candidate reference gene (Tran et al., ). In addition, extremely low C q values lead to technical difficulties with baseline correction of the amplification curves (data not shown).…”

“…Reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR) has been used to understand the impact of nutritional and other factors on the expression of microcystin genes. For instance, the influence of micro-and macronutrients on mcyD expression was investigated (Kuniyoshi, Sevilla, Bes, Fillat, & Peleato, 2013;Pimentel & Giani, 2014;Sevilla et al, 2008Sevilla et al, , 2010, and the effect of high light stress as well as co-occurring cyanobacteria and cell concentration on mcyE expression was studied (Ngwa, Madramootoo, & Jabaji, 2014;Tran, Bernard, Ammar, Chaouch, & Comte, 2013;Wood et al, 2011).…”

Transcriptomic Responses in the Bloom-Forming Cyanobacterium Microcystis Induced during Exposure to Zooplankton

“…Other heat shock protein genes surveyed by Rhee et al were not responsive to high temperature, suggesting other stress response roles ( 53 ). In Planktothrix agardhii , the abundances of transcripts for dnaK , groEL , and groES (heat shock protein 70 and chaperonin genes, respectively) increased under high light conditions, suggesting roles in oxidative stress defense ( 54 ), as oxidative stress often promotes the expression of molecular chaperones and proteases ( 55 ). The temperature in this study was maintained at 21°C, demonstrating that the increased expression for this class of genes was unrelated to temperature.…”

Cloning of some heat shock proteins genes for further transcriptional study of Planktothrix agardhii exposed to abiotic stress

“…In the complex response of cyanobacteria to abiotic stress, the activities of Hsps play important roles. Cyanobacteria produce different types of Hsps upon exposure to stress (Bergmann et al 2010;Tran et al 2013;Webb et al 1990;Webb and Sherman 1994). The five main classes of Hsps are discovered to be present in cyanobacteria (Wase et al 2013).…”

“…If MC have protective role in cells facing stressful stimuli, we speculate that the expression of genes coding for Hsps might be different in an MCproducing strain and its MC-deficient mutant. To test this hypothesis, the expressions of hsp genes of an MCproducing strain and its MC-deficient mutant over different periods of exposure to abiotic stress, such as high light stress (Tran et al 2013), can be compared using reverse transcription quantitative PCR (RT-qPCR). However, prior to investigating such a stress response analysis, a first step in the isolation of hsp genes (i.e., gene of interest (GOI)) is prerequisite, as the genome of Planktothrix agardhii has not been fully sequenced yet.…”