肉苁蓉-梭梭寄生系统中转移mRNA的鉴定及其功能探究

As an endangered species, Cistanche deserticola was known as “desert Ginseng” because of its high medicinal value. Cistanche deserticola is perennial obligate parasitic herb and is belonged to Orobanchaceae. Cistanche deserticola parasites on the roots of Halaxylon ammodendron, a drought resistant plant belonging to Chenopodiacea. It was reported that chloroplast rpoC2 gene was transferred from Halaxylon ammodendron to Cistanche deserticola by horizontal gene transfer. Previously, we identified nearly 1000 mobile mRNA between Cistanche deserticola and Haloxylon ammodendron through next-generation transcriptome sequencing and bioinformatics analysis. In this study, we will perform full-length transcriptome sequencing on Cistanche deserticola and Haloxylon ammodendron to enrich their sequence information and reveal the full-length cDNA sequence of the transfer mRNA. The mobile mRNA will be ascertained by multiple sequence alignment, comparison with the previously identified transfer mRNA, application of N. Benthemiana-dodder parasitic system and comparison with the phloem RNA sequence. The character, function and trend of mobile mRNA will be investigated. To date, reports on signal molecule exchange between host and parasite were very limited, and the research was only conducted on the model system like Arabidopsis and tomato. The present study has important theoretical implication and potent application value, as it is the first of such study using herbaceous medicinal plant like Cistanche deserticola and it is also the one to investigate parasitic mechanism from the view of mobile mRNA.

肉苁蓉属CITES附录Ⅱ保护物种，素有“沙漠人参”之美誉，具有极高的药用价值。肉苁蓉是专性寄生草本植物，属于列当科，寄生于藜科植物梭梭的根部，而梭梭是抗旱固沙植物，也是国家级保护植物。肉苁蓉和梭梭间叶绿体rpoC2基因的水平基因转移已有报道，前期研究中我们也通过二代转录组测序及生物信息学分析鉴定了近千个肉苁蓉和梭梭间的转移mRNA。本研究中，拟对肉苁蓉及梭梭进行三代全长转录组测序，从而丰富其序列信息，并找到转移mRNA的全长cDNA序列。通过多重序列比对、与上述鉴定的转移mRNA的比较、异源寄生体系的验证及与韧皮部RNA的比较来来确认转移mRNA并探讨可移动mRNA的特征及功能等。目前，寄生植物-宿主间信息分子交换的研究非常少，仅有的例子也使用了菟丝子及模式植物宿主拟南芥等。所以，我们首次对根部寄生的草本植物肉苁蓉进行此类研究，旨在从转移mRNA角度探讨其寄生机理，具有非常重要的研究意义。

肉苁蓉（Cistanche deserticola Y. C. Ma.）是我国名贵的中草药材，素有“沙漠人参”的美誉。肉苁蓉是列当科（Orobanchaceae.）植物，通常寄生于藜科（Chenopodiaceae.）植物梭梭（Haloxylon ammodendron (C. A. Mey.) Bunge.）的根部。肉苁蓉独特的生长特性以及低萌发率的特点严重影响其与宿主梭梭的寄生关系建立，因此肉苁蓉种子萌发机理的研究具有重要意义。本项目首先进行了肉苁蓉种子萌发实验并以早期发芽种子为材料探究了肉苁蓉种子萌发过程的相关基因，从种子萌发差异表达的基因中重点分析了与细胞壁分解重排及水解酶相关的基因，发现CdXTH33、CdBXL1及CdEP3三个基因在宿主向日葵根部的异源过表达提高了向日葵列当的寄生率，暗示这三个基因在荒漠肉苁蓉中也可能具有促进寄生的功能。. 有研究发现宿主和茎寄生植物之间有 mRNA 的交换，但根寄生植物中鲜有报道。我们使用转录组测序和生物信息学分析鉴定了梭梭-肉苁蓉之间近1万个转移 mRNA。转录本丰度是促使转移事件的驱动力，且mRNA 交换通过吸器来发生。这些mRNA 的转移在肉苁蓉-梭梭之间和向日葵-列当异源寄生系统中得到了证实。五个肉苁蓉→梭梭移动 mRNA 促进了吸器的发育。有趣的是，两个基因 CdNLR1 和 CdNLR2 的转移 mRNA 引起根特异性超敏反应并延迟寄生植物的发育，这可能有助于寄生-生存之间的平衡。本研究为木本宿主和根寄生植物之间的大规模 mRNA 转移事件提供了证据，并证明了七个肉苁蓉基因在宿主-寄生植物相互作用中的相关功能。迄今为止，关于宿主和寄生植物之间功能性 mRNA 交换的报道非常有限。因此，我们的研究从移动 mRNA 的角度提供了新的对寄生机制的见解。