Genome-Scale Transcriptome Analysis of the Desert Shrub Artemisia sphaerocephala

BackgroundArtemisia sphaerocephala, a semi-shrub belonging to the Artemisia genus of the Compositae family, is an important pioneer plant that inhabits moving and semi-stable sand dunes in the deserts and steppes of northwest and north-central China. It is very resilient in extreme environments. Additionally, its seeds have excellent nutritional value, and the abundant lipids and polysaccharides in the seeds make this plant a potential valuable source of bio-energy. However, partly due to the scarcity of genetic information, the genetic mechanisms controlling the traits and environmental adaptation capacity of A. sphaerocephala are unknown.ResultsHere, we present the first in-depth transcriptomic analysis of A. sphaerocephala. To maximize the representation of conditional transcripts, mRNA was obtained from 17 samples, including living tissues of desert-growing A. sphaerocephala, seeds germinated in the laboratory, and calli subjected to no stress (control) and high and low temperature, high and low osmotic, and salt stresses. De novo transcriptome assembly performed using an Illumina HiSeq 2500 platform resulted in the generation of 68,373 unigenes. We analyzed the key genes involved in the unsaturated fatty acid synthesis pathway and identified 26 A. sphaerocephala fad2 genes, which is the largest fad2 gene family reported to date. Furthermore, a set of genes responsible for resistance to extreme temperatures, salt, drought and a combination of stresses was identified.ConclusionThe present work provides abundant genomic information for functional dissection of the important traits of A. sphaerocephala and contributes to the current understanding of molecular adaptive mechanisms of A. sphaerocephala in the desert environment. Identification of the key genes in the unsaturated fatty acid synthesis pathway could increase understanding of the biological regulatory mechanisms of fatty acid composition traits in plants and facilitate genetic manipulation of the fatty acid composition of oil crops.研究背景 黑沙蒿（Artemisia sphaerocephala）是隶属于菊科（Compositae）蒿属（Artemisia）的半灌木，为中国西北及中北部沙漠与草原地区流动、半固定沙丘上的重要先锋植物，对极端环境具备极强的耐受能力。此外，其种子拥有优异的营养价值，种子中富含的脂质与多糖使其成为极具潜力的生物质能源珍贵原料。然而，受限于遗传信息匮乏，目前学界对黑沙蒿调控其性状与环境适应能力的遗传机制仍一无所知。 研究结果 本研究首次对黑沙蒿开展了系统性的深度转录组分析。为最大限度覆盖不同条件下的转录本，研究团队从17份样本中提取了mRNA，样本包括野外沙漠生境下黑沙蒿的活体组织、实验室萌发的种子，以及经无胁迫（对照）、高低温、高低渗透及盐胁迫处理的愈伤组织。依托Illumina HiSeq 2500平台完成的从头转录组组装，共得到68373条单基因（unigene）。本研究对不饱和脂肪酸合成通路中的关键基因进行了分析，共鉴定出26个黑沙蒿fad2基因家族成员，为目前已报道的规模最大的fad2基因家族。此外，本研究还筛选得到一批参与极端温度、盐渍、干旱及复合胁迫抗性调控的基因。 研究结论 本研究为黑沙蒿重要性状的功能解析提供了丰富的组学数据，也有助于进一步阐明黑沙蒿适应沙漠环境的分子调控机制。对不饱和脂肪酸合成通路关键基因的鉴定，可加深学界对植物脂肪酸组成性状生物学调控机制的理解，同时为油料作物脂肪酸组成的遗传改良提供理论支撑。