Transcriptional Responses of the Heat Shock Protein 20 (Hsp20) and 40 (Hsp40) Genes to Temperature Stress and Alteration of Life Cycle Stages in the Harmful Alga Scrippsiella trochoidea (Dinophyceae)

SIMPLE SUMMARY: As the greatest contributors to harmful algal blooms, dinoflagellates account for roughly 75% of bloom events, which become an escalating threat to coastal ecosystems and cause substantial economic loss worldwide. Resting cyst production and broad temperature tolerance are well proven as adaptive strategies for blooming dinoflagellates; however, to date, the underlying molecular information is scarce. In the present study, we characterized two heat shock protein genes from the representative dinoflagellate Scrippsiella trochoidea, with the aim to primarily determine their possible roles in response to temperature stress and alteration of the life cycle. The yielded results enhance our knowledge about the functions of cross-talk of different Hsp members in temperature adaptation of dinoflagellates and facilitate further exploration in their potential physiological relevance during different life-stage alternation in this ecological important lineage. ABSTRACT: The small heat shock protein (sHsp) and Hsp40 are Hsp members that have not been intensively investigated but are functionally important in most organisms. In this study, the potential roles of a Hsp20 (StHsp20) and a Hsp40 (StHsp40) in dinoflagellates during adaptation to temperature fluctuation and alteration of different life stages were explored using the representative harmful algal blooms (HABs)-causative dinoflagellate species, Scrippsiella trochoidea. We isolated the full-length cDNAs of the two genes via rapid amplification of cDNA ends (RACE) and tracked their differential transcriptions via real-time qPCR. The results revealed StHsp20 and StHsp40 exhibited mRNA accumulation patterns that were highly similar in response to heat stress but completely different toward cold stress, which implies that the mechanisms underlying thermal and cold acclimation in dinoflagellates are regulated by different sets of genes. The StHsp20 was probably related to the heat tolerance of the species, and StHsp40 was closely involved in the adaptation to both higher and lower temperature fluctuations. Furthermore, significantly higher mRNA abundance of StHsp40 was detected in newly formed resting cysts, which might be a response to intrinsic stress stemmed from encystment. This finding also implied StHsp40 might be engaged in resting cyst formation of S. trochoidea. Our findings enriched the knowledge about possible cross-talk of different Hsp members in dinoflagellates and provided clues to further explore the molecular underpinnings underlying resting cyst production and broad temperature tolerance of this group of HABs contributors.