Priming-induced transcriptome response to heat stress in young sugar kelp sporophytes
This study examines how warm temperature priming of Saccharina latissima gametophytes influences the transcriptomic responses and physiological performance of young sporophytes under heat stress. By combining RNA sequencing with physiological measurements, the research aims to uncover whether thermal priming enhances stress tolerance and the underlying gene expression changes associated with this process.  Experimental Setup The study began by priming Saccharina latissima gametophytes for three weeks at two distinct temperatures. Gametophytes exposed to 10°C served as the control group, representing ambient environmental conditions. A parallel group was exposed to 20°C to simulate a warm-priming condition. After the priming phase, the gametophytes were cultured into young sporophytes under controlled conditions in a fitotron growth chamber at Mørkvedbukta.  The young sporophytes were cultivated in sterile Provasoli Enriched Seawater (PES) within three replicate beakers for each treatment. In each beaker, 12 sporophytes were grown and later 3 pooled at each of 4 time points to ensure adequate sample sizes for physiological and molecular analyses.  Heat Stress Experiment The stress experiment, conducted in March 2024, tested the responses of primed and non-primed sporophytes to a controlled heat stress protocol. Initially, samples were collected from the sporophytes before the onset of heat stress, when the temperature was still at 10°C. Subsequently, the temperature was gradually increased to 21.5°C over four days, and another set of samples was collected at this peak stress condition. Following the peak, the temperature was decreased slowly back to 10°C over a period of three days (from Day 5 to Day 8). Final samples were collected on Day 10 to evaluate recovery dynamics. This design allowed the study to capture gene expression changes and physiological responses across baseline, acute stress, and recovery phases.  Data Collection and Analysis To understand the molecular responses, RNA was extracted from the sporophyte samples and sent to Novogene for sequencing. Total RNA libraries were prepared through RNA depletion, retaining both messenger RNA (mRNA) and long non-coding RNA (lncRNA). These libraries provided insights into the transcriptional activity associated with temperature priming and heat stress.  In addition to transcriptomic data, photosynthetic performance was measured using a PAM fluorometer (PSI handheld model). This approach allowed the researchers to assess changes in photosynthetic efficiency, a key indicator of physiological stress and recovery in plants.  Research Questions This study seeks to address two main questions: How does temperature priming of gametophytes influence the physiological performance of young sporophytes during and after heat stress? Furthermore, what are the transcriptomic responses underlying the observed performance differences between primed and non-primed sporophytes?  Significance By integrating physiological performance measurements with transcriptomic analyses, this study provides valuable insights into the potential benefits of thermal priming in Saccharina latissima. Understanding how priming affects stress tolerance and recovery mechanisms at both the molecular and physiological levels has important implications for sustainable aquaculture and the resilience of kelp populations in the face of climate change. The findings could inform strategies to enhance the heat tolerance of kelp, a critical species in marine ecosystems and commercial cultivation.