Proline accumulation is an important mechanism for osmotic regulation under salt stress. In this study, we evaluated proline accumulation profiles in roots, stems and leaves of Jerusalem artichoke (Helianthus tuberosus L.) plantlets under NaCl stress. We also examined HtP5CS, HtOAT and HtPDH enzyme activities and gene expression patterns of putative HtP5CS1, HtP5CS2, HtOAT, HtPDH1, and HtPDH2 genes. The objective of our study was to characterize the proline regulation mechanisms of Jerusalem artichoke, a moderately salt tolerant species, under NaCl stress. Jerusalem artichoke plantlets were observed to accumulate proline in roots, stems and leaves during salt stress. HtP5CS enzyme activities were increased under NaCl stress, while HtOAT and HtPDH activities generally repressed. Transcript levels of HtP5CS2 increased while transcript levels of HtOAT, HtPDH1 and HtPDH2 generally decreased in response to NaCl stress. Our results supports that for Jerusalem artichoke, proline synthesis under salt stress is mainly through the Glu pathway, and HtP5CS2 is predominant in this process while HtOAT plays a less important role. Both HtPDH genes may function in proline degradation.

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The interaction between roots and bacterial communities in halophytic species is poorly understood. Here, we used Jerusalem artichoke cultivar Nanyu 1 (NY-1) to characterise root distribution patterns and determine diversity and abundance of bacteria in the rhizosphere soil under variable salinity. Root growth was not inhibited within the salinity range 1.2 to 1.9 g salt/kg, but roots were mainly confined to 0–20 cm soil layer vertically and 0–30 cm horizontally from the plant centre. Root concentrations of K+, Na+, Mg2+ and particularly Ca2+ were relatively high under salinity stress. High salinity stress decreased soil invertase and catalase activity. Using a next-generation, Illumina-based sequencing approach, we determined higher diversity of bacteria in the rhizosphere soil at high than low salinity. More than 15,500 valid reads were obtained, and Proteobacteria, Acidobacteria, Bacteroidetes and Actinobacteria predominated in all samples, accounting for >80% of the reads. On a genus level, 636 genera were common to the low and high salinity treatments at 0–5 cm and 5–10 cm depth. The abundance of Steroidobacter and Sphingomonas was significantly decreased by increasing salinity. Higher Shannon and Chao 1 indices with increasing severity of salt stress indicated that high salt stress increased diversity in the bacterial communities.

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a b s t r a c tThe biggest challenge for the production of bulk commodities such as biofuels and bio-based chemicals through biorefinery is to secure low-cost biomass feedstocks on a large scale. Current sugar-and starchbased feedstocks are not sustainable due to their main usage as food or food ingredients for humans. Although lignocellulosic biomass, particularly agricultural residues, is abundantly available, its conversion and utilization are still not economically competitive. One solution is to develop specific energy crops that can grow well on marginal land without competing for arable land with grain production. Jerusalem artichoke (Helianthus tuberosus L.) is tolerant to environmental stresses such as drought and salinity as well as plant diseases, and thus is an alternative energy crop. The biomass of Jerusalem artichoke comes mainly from its tubers containing inulin as a major component, which can be hydrolyzed into fermentable sugars without an energy-intensive pretreatment. In this article, genetic resources, cultivar selection and planting of Jerusalem artichoke are reviewed. Compared to other herbaceous energy crops, particularly switchgrass and Miscanthus that have been intensively studied in the United States and Europe, not only can Jerusalem artichoke be used as feedstock for producing biofuels and bio-based chemicals, but also value-added products to make the biorefinery process more economically competitive.

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