Priming as a kelp engineering technology to enhance yield and secure production under environmental challenges

Kelp farming is a promising blue industry in Europe. However, global rising ocean temperatures could make kelp farming unsustainable. Thus one major current challenge in this industry is to breed or genetically engineer heat-resistant strains. However, breeding requires repeated selection over several generations (and thereby needs many years) and also reduces genetic diversity that insures against unforeseen environmental challenges; while gene modified organisms are not allowed to be grown in the sea in Europe. The KELPRIME project aims to engineer robust and heat-resistant kelp without altering its genetic makeup and diversity. We adopt a technique from agriculture termed 'priming' that enhances yield and stress resistance in crop plants. To 'prime', small life-cycle stages are deliberately exposed to extreme low and high temperatures. Similar to vaccination that boosts an immune response, priming likely boosts defense/resilience mechanisms in plants. If this is transferable to kelp, the kelp fronds could then activate response mechanisms faster, stronger, or earlier when meeting the stress again. We have assembled a multi-disciplinary team with expertise in kelp ecology and cultivation, molecular biology, and genomics, in order to test for the build-up and stability of a priming memory, which is supposedly based on epigenetic marks, and that could transfer induced heat resistance, and/or improved performance such as enhanced growth, within or across generations. Ecological niche modeling further shows that even small increases in thermal tolerance could rescue large areas of coastline for future kelp farming. For example, enhancing thermal tolerance by 1–3°C through priming could maintain or expand suitable farming habitat in Europe despite ocean warming. Our initial research on Saccharina latissima revealed intriguing complexities in the effects of thermal priming. While warm priming of gametophytes (20°C for 3 weeks) did significantly enhance the survival of young sporophytes, this effect unfortunately did not persist into the adult, harvestable sporophytes. Furthermore, these warm-primed adult sporophytes displayed increased susceptibility to urchin grazing compared to non-primed kelp. On the other hand, adult sporophytes rapidly and positively responded to short term sub-lethal heat priming with increased survival capacities at high temperatures. At the molecular level, transcriptome analyses now show that warm-primed S. latissima sporophytes mount a stronger response when re-exposed to heat stress (more genes are induced). The priming treatment altered gene regulation, with differences in protein phosphorylation pathways and long non-coding RNAs. This indicates that priming establishes a molecular stress memory that reprograms how kelp responds to later stress. We are also exploring epigenetic mechanisms such as DNA methylation that may explain how stress tolerance can be memorized and even transmitted across generations. Interestingly, our research also revealed unexpected benefits of cold priming (exposure of gametophyte cultures to 0°C for 3 weeks). Cold priming significantly enhanced the vegetative growth of gametophytes and led to increased length and density of the derived sporophytes in S. latissima. Remarkably, this translated to a doubling of kelp yield, reaching approximately 1 kg fresh weight per meter of rope, compared to non-primed sporophytes. Similarly, in the kelp Alaria esculenta, cold-priming of gametophytes also enhanced sporophyte production in low sub-optimum temperatures compared to controls, but warm priming did not enhance the recruitment at sub-otimum high temperatures. Our ongoing experiments highlight that priming effects depend strongly on life stage, investigated process and cultivation duration. Long-term trials with Alaria esculenta growing sporophytes over several months indicate that growth response pattern completely differ to short-term experiments with juvenile sporophytes. Thus it may not always be easy to predict the performance of older sporophytes unless tested across full seasonal cycles, underlining the need to study the entire life cycle to understand priming effects in mariculture and nature. These findings highlight the potential of priming, as a valuable tool for enhancing kelp aquaculture yield, but with differential effects induced by warm or cold priming. We are now pursuing further research to fully understand the mechanisms underlying the observed effects. In the last project year we focus on dissemination, communication, and exploitation to integrate priming strategies into kelp hatcheries for long-term benefits to kelp farming.

Rising ocean temperatures are compromising the health and growth of macroalgae and, thus, threaten the production security of farmed macroalgae commodities with an annual value of $US 13.3 billion. While 97% of the global macroalgae biomass is produced in Asia, farming of macroalgae (particularly kelp) is becoming a new bioeconomy sector in Europe and the Americas, where it decreases harvesting pressure on wild stocks, and provides new job opportunities. However, economic losses after heat events can make this budding industry unsustainable. While kelp breeding allows to develop superior cultivars, the associated reduction in genetic diversity often leads to poor performance and productivity under environmental challenges. Moreover, breeding is a long-term process that requires artificial selection over several generations. In order to secure production under environmental challenges, the KELPRIME project aims to establish ‘priming’, a common technique to rapidly enhance yield and stress resistance in crop agriculture, as a novel bio-engineering technique in kelp cultivation. We have assembled an interdisciplinary team combining expertise in kelp cultivation, farming and development with unique molecular skills and resources to characterize positive priming effects in the cultivation of two commercially important kelp species, and to test for the first time whether these effects rely primarily on the formation of an epigenetic stress memory. Without knowing the mechanisms underlying positive priming effects, priming can’t be commercially exploited as novel kelp engineering technology. If successful, this work will be a milestone in sustainable bio-engineering and strain improvement of macroalgae, leading to high-profile publications, and igniting research lines aiming to exploit the wide application potential of priming.