紫菜腐霉激发子基因家族特征及其在感染过程中的作用

Characteristics of elicitin gene family of Pythium porphyrae and its role in infection

摘要:

[背景] 激发子（elicitin）是卵菌（Oomycetes）疫霉和腐霉分泌的可诱发宿主产生免疫反应的小分子化合物。[目的] 鉴定紫菜腐霉激发子基因家族，分析其结构特征和在感染宿主过程中可能的作用机制。[方法] 运用同源比对法筛查紫菜腐霉NBRC33253基因组中激发子基因家族成员，利用生物信息学工具分析激发子家族的理化性质和系统进化，并结合转录组数据和GO功能注释，探讨其在感染宿主过程中可能的作用机制。[结果] 紫菜腐霉基因组中发现22个激发子基因家族成员，其中，17个为胞外分泌蛋白，4个定位于质膜，1个锚定于高尔基体。紫菜腐霉激发子基因结构简单保守，含有1-2个CDS序列，每个成员基因编码的氨基酸数目介于114-2 100 aa之间，等电点PI在3.61-9.88之间；系统进化分析显示，紫菜腐霉激发子家族成员存在扩张；表达模式分析说明，紫菜腐霉激发子在感染宿主后6个激发子基因表达量上调，7个激发子基因表达量下调，推测可能具有多个生物学功能，如GO功能注释到纤维素结合激发子凝集素（cellulose binding elicitor lectin，CBEL）和共生体对宿主防御相关程序性细胞死亡的调节过程。[结论] 紫菜腐霉激发子基因家族结构保守，均属于ELL （elicitin-like）亚类，可能具有纤维素结合激发子凝集素（CBEL）和加速宿主细胞程序性死亡的功能，结合纤维素，附着在宿主表面，发挥蛋白激酶活性，触发宿主MAPK信号传导通路介导的免疫反应，促进HR细胞死亡。本研究为进一步解析紫菜腐霉的致病机制及紫菜抗病性状的遗传育种提供了理论基础。

Abstract:

[Background] Elicitin is small molecule compound secreted by the Oomycetes Phytophthora and Pythium that can induce immune response in the host. [Objective] Identify the elicitin gene family of Pythium porphyrae and analyze its structural features and possible mechanisms of action during the infection. [Methods] Screening the genome of Pythium porphyrae NBRC33253 for members of elicitin gene family using homologous alignment method. Analysis of the physicochemical properties and phylogeny of elicitin family using bioinformatics tools, combined with transcriptomic data and GO functional annotation to discuss possible mechanism of action during the infection. [Results] Twenty-two elicitin gene family members were identified in the Pythium porphyrae genome. 17 elicitin genes were extracellular secretory proteins, four were localized at the plasma membrane and one was anchored to the Golgi apparatus. The elicitin genes are simple and conserved in structure, containing 1-2 CDS sequences, with the number of amino acids ranging from 114 to 2 100 aa and the isoelectric point ranging from 3.61 to 9.88. The phylogenetic analysis revealed an expansion of elicitin family in Pythium porphyrae NBRC33253. Expression analysis showed that six elicitin genes was up-regulated and seven elicitin genes down-regulated after infection, indicating Pythium porphyrae elicitin gene presumably possessed multiple biological functions. As annotated by GO function to cellulose binding elicitor lectin (CBEL) and modulation by symbiont of host defense-related programmed cell death. [Conclusion] The elicitin gene family of Pythium porphyrae is structurally conserved and belongs to the ELL (elicitin-like) subfamily. Due to the annotation, elicitins in NBRC33253 showed several kinds of function, including cellulose binding excitor lectin (CBEL) which could accelerate programmed cell death in host cells by binding cellulose, attaching to the host surface, performing protein kinase activity, triggering host MAPK signaling pathway-mediated immune responses, and promoting HR cell death. This study provides theoretical basis for further elucidation of the pathogenic mechanism of Phythium porphyrae and genetic breeding for disease resistance traits in Pyropia.