Maintenance of grafting‐induced epigenetic variations in the asexual progeny of Brassica oleracea and B. juncea chimera
Maintenance of grafting‐induced epigenetic variations in the asexual progeny of Brassica oleracea and B. juncea chimera
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DOI：
10.1111/tpj.14058
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发表时间：
2018-09
期刊：
影响因子：
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通讯作者：
Ningning Yu;Liwen Cao;Lu Yuan;Xiao Zhi;Yiqian Chen;S. Gan;Liping Chen
中科院分区：
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作者：
Ningning Yu;Liwen Cao;Lu Yuan;Xiao Zhi;Yiqian Chen;S. Gan;Liping Chen
嫁接引起的变异已经在许多植物物种中观察到，但后代变异的遗传力还不是很清楚。在我们的研究中，从茎尖分生组织(SAM)的C细胞谱系嫁接嵌合体TCC(其中SAM的最外、中和最内层的细胞层的起源分别用‘T’表示块茎芥菜和‘C’表示红甘蓝)诱导不定芽，并鉴定为r-CCC(r=再生)。为了研究细胞增殖和再生过程中嫁接变异的维持，通过r-CCCN腋芽的连续再生，建立了不同世代的无性后代(r-CCCN，n=世代)。选择第四代r-CCC4(r-CCC4)进行全基因组测序，比较分析异种嫁接引起的甲基化变化与r-S-CCC4(S=自体嫁接)的差异。在r-CCC4中观察到CHH甲基化水平和比例增加，重复元件发生重大变化。小RNA测序发现1135个特异性小干扰RNA(SiRNA)标签，这些标签通常在r-CCC、r-CCC2和r-CCC4中表达。值得注意的是，其中65%的特定siRNAs与重复元件相关，称为RE siRNAs。随后的分析表明，RE siRNA重叠区的CHH甲基化主要是r-CCC4中的超甲基化，表明它们负责指导和维持嫁接诱导的CHH甲基化。此外，13个差异甲基化基因(DMG)的表达与表型变异相关，表明r-CCC4和r-S-CCC4的表达水平存在差异。这些DMG主要是CG高甲基化，它们的甲基化修饰对应于相对甲基转移酶的转录。
Grafting-induced variations have been observed in many plant species, but the heritability of variation in progeny is not well understood. In our study, adventitious shoots from the C cell lineage of shoot apical meristem (SAM) grafting chimera TCC (where the origin of the outmost, middle and innermost cell layers, respectively, of SAM is designated by 'T' for tuber mustard and 'C' for red cabbage) were induced and identified as r-CCC (r = regenerated). To investigate the maintenance of grafting variations during cell propagation and regeneration, different generations of asexual progeny (r-CCCn, n = generation) were established through successive regeneration of axillary shoots from r-CCC. The fourth generation of r-CCC (r-CCC4) was selected to perform whole genome bisulfite sequencing for comparative analysis of hetero-grafting-induced global methylation changes relative to r-s-CCC4 (s = self-grafting). Increased CHH methylation levels and proportions were observed in r-CCC4, with substantial changes occurring in the repeat elements. Small RNA sequencing revealed 1135 specific small interfering RNA (siRNA) tags that were typically expressed in r-CCC, r-CCC2 and r-CCC4. Notably, 65% of these specific siRNAs were associated with repeat elements, termed RE siRNAs. Subsequent analysis revealed that the CHH methylation of RE siRNA-overlapping regions was mainly hypermethylation in r-CCC4, indicating that they were responsible for directing and maintaining grafting-induced CHH methylation. Moreover, the expression of 13 differentially methylated genes (DMGs) correlated with the phenotypic variation, showing differential expression levels between r-CCC4 and r-s-CCC4. These DMGs were predominantly CG hypermethylated, their methylation modifications corresponded to the transcription of relative methyltransferase.