In comparison with retrotransposons, DNA transposons make up a smaller proportion of most plant genomes. However, these elements are often proximal to genes to affect gene expression depending on the activity of the transposons, which is largely reflected by the activity of the transposase genes. Here, we show that three AT‐rich introns were retained in the TNP2‐like transposase genes of the Bot1 (Brassica oleracea transposon 1) CACTA transposable elements in Brassica oleracea, but were lost in the majority of the Bot1 elements in Brassica rapa. A recent burst of transposition of Bot1 was observed in B. oleracea, but not in B. rapa. This burst of transposition is likely related to the activity of the TNP2‐like transposase genes as the expression values of the transposase genes were higher in B. oleracea than in B. rapa. In addition, distinct populations of small RNAs (21, 22 and 24 nt) were detected from the Bot1 elements in B. oleracea, but the vast majority of the small RNAs from the Bot1 elements in B. rapa are 24 nt in length. We hypothesize that the different activity of the TNP2‐like transposase genes is likely associated with the three introns, and intron loss is likely reverse transcriptase mediated. Furthermore, we propose that the Bot1 family is currently undergoing silencing in B. oleracea, but has already been silenced in B. rapa. Taken together, our data provide new insights into the differentiation of transposons and their role in the asymmetric evolution of these two closely related Brassica species.

中文翻译：

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CACTA转座酶基因的分析揭示了芸苔基因组差异进化的内含子丢失和独特的小RNA沉默途径的机制

与反转录转座子相比，DNA转座子在大多数植物基因组中所占的比例较小。然而，取决于转座子的活性，这些元件通常最接近基因以影响基因表达，这在很大程度上由转座酶基因的活性反映。在这里，我们显示，三AT-丰富内含子被保留在TNP2般的的转基因Bot1（甘蓝转1）在CACTA转座子甘蓝，但是在大多数的丢失Bot1中的元素芜菁。在甘蓝芽孢杆菌中观察到Bot1转座的最近爆发，而在番茄中没有发生。芜菁。换位的该突发可能与所述的活性TNP2样转基因作为转座的基因的表达值在更高甘蓝比芜菁。此外，从所检测到的小RNA（21，22和24个核苷酸）的不同群体Bot1中的元素甘蓝，但绝大多数来自小RNA的Bot1在元件芜菁是24个核苷酸的长度。我们假设TNP2的不同活性像转座酶的基因可能与三个内含子有关，而内含子的丢失很可能是逆转录酶介导的。此外，我们建议Bot1家族目前在经受沉默甘蓝，但已经在被压制芜菁。综上所述，我们的数据为转座子的分化及其在这两个密切相关的芸苔属植物的不对称进化中的作用提供了新的见解。