Ulva proliferais the dominant species of “green tide”, and has higher tolerance to environmental stresses such as temperature. However, the molecular mechanisms are still unclear. Here, transcriptome analysis, Western blot and RT-qPCR analysis ofU. proliferasuggested that, under temperature stresses (4°C, 36°C), the expression ofPCNAandCyclinAwas promoted, and the MAPK signaling was activated. Besides, the results showed that PCNA interacted with CyclinA. Interestingly, the expression ofmiR-2916, which was predicted to bind PCNA at -552∼-772, was negatively correlated with the expression ofPCNAunder temperature stresses (4°C, 36°C). In addition, the results showed that low temperature (4°C) had no obvious effect on the survival, the formation of cell walls, and the division of protoplasts. However, high temperature (36°C) had obvious effect on them. PCNA inhibitors increased the sensitivity of the protoplasts under temperature stresses. Together, our results suggested PCNA regulating the proliferation in response to the temperature stress ofU. proliferawas associated with miR-2916/PCNA/CyclinA/MAPK pathway. In conclusion, the study preliminarily illuminates the molecular mechanism in response to temperature stress ofU. prolifera, and may provide a new insight for prevention of green tide.

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As an economically valuable red seaweed, Neopyropia yezoensis (Rhodophyta) is cultivated in intertidal areas, and its growth and development are greatly influenced by environmental factors such as temperature. Although much effort has been devoted to delineating the influence, the underlying cellular and molecular mechanisms remain elusive. In this study, the gametophyte blades and protoplasts were cultured at different temperatures (13 °C, 17 °C, 21 °C, 25 °C). Only blades cultured at 13 °C maintained a normal growth state (the relative growth rate of thalli was positive, and the content of phycobiliprotein and pigments changed little); the survival and division rates of protoplasts were high at 13 °C, but greatly decreased with the increase in temperature, suggesting that 13 °C is suitable for the growth of N. yezoensis. In our efforts to delineate the underlying mechanism, a partial coding sequence (CDS) of Cyclin B and the complete CDS of cyclin-dependent-kinase B (CDKB) in N. yezoensis were cloned. Since Cyclin B controls G2/M phase transition by activating CDK and regulates the progression of cell division, we then analyzed how Cyclin B expression in the gametophyte blades might change with temperatures by qPCR and Western blotting. The results showed that the expression of Cyclin B first increased and then decreased after transfer from 13 °C to higher temperatures, and the downregulation of Cyclin B was more obvious with the increase in temperature. The phosphorylation of extracellular signal-regulated kinase (ERK) decreased with the increase in temperature, suggesting inactivation of ERK at higher temperatures; inhibition of ERK by FR180204 significantly decreased the survival and division rates of protoplasts cultured at 13 °C. These results suggest that downregulation of Cyclin B and inactivation of ERK might be involved in negatively regulating the survival and division of protoplasts and the growth of gametophyte blades of N. yezoensis at high temperatures.