Laboratory of Plant Developmental Genetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, v,v,i,Kralovopolska 135, CZ-612 65 Brno, Czech Republic.
BMC Plant Biol. 2010 Aug 18;10:180. doi: 10.1186/1471-2229-10-180.
The evolution of sex chromosomes is often accompanied by gene or chromosome rearrangements. Recently, the gene AP3 was characterized in the dioecious plant species Silene latifolia. It was suggested that this gene had been transferred from an autosome to the Y chromosome.
In the present study we provide evidence for the existence of an X linked copy of the AP3 gene. We further show that the Y copy is probably located in a chromosomal region where recombination restriction occurred during the first steps of sex chromosome evolution. A comparison of X and Y copies did not reveal any clear signs of degenerative processes in exon regions. Instead, both X and Y copies show evidence for relaxed selection compared to the autosomal orthologues in S. vulgaris and S. conica. We further found that promoter sequences differ significantly. Comparison of the genic region of AP3 between the X and Y alleles and the corresponding autosomal copies in the gynodioecious species S. vulgaris revealed a massive accumulation of retrotransposons within one intron of the Y copy of AP3. Analysis of the genomic distribution of these repetitive elements does not indicate that these elements played an important role in the size increase characteristic of the Y chromosome. However, in silico expression analysis shows biased expression of individual domains of the identified retroelements in male plants.
We characterized the structure and evolution of AP3, a sex linked gene with copies on the X and Y chromosomes in the dioecious plant S. latifolia. These copies showed complementary expression patterns and relaxed evolution at protein level compared to autosomal orthologues, which suggests subfunctionalization. One intron of the Y-linked allele was invaded by retrotransposons that display sex-specific expression patterns that are similar to the expression pattern of the corresponding allele, which suggests that these transposable elements may have influenced evolution of expression patterns of the Y copy. These data could help researchers decipher the role of transposable elements in degenerative processes during sex chromosome evolution.
性染色体的进化通常伴随着基因或染色体的重排。最近，在雌雄异株植物石竹属植物中鉴定出了 AP3 基因。有人提出，这个基因是从常染色体转移到 Y 染色体上的。
在本研究中，我们提供了存在 AP3 基因 X 连锁拷贝的证据。我们进一步表明，Y 拷贝可能位于性染色体进化早期发生重组限制的染色体区域。X 和 Y 拷贝的比较没有显示出外显子区域退化过程的任何明显迹象。相反，与 S. vulgaris 和 S. conica 的常染色体直系同源物相比，X 和 Y 拷贝都显示出选择放松的迹象。我们进一步发现启动子序列有显著差异。比较雌雄同体的石竹属植物 X 和 Y 等位基因和相应的常染色体拷贝的 AP3 基因的基因区域，发现 Y 拷贝的 AP3 基因的一个内含子中大量积累了逆转录转座子。这些重复元件的基因组分布分析表明，这些元件在 Y 染色体大小增加的特征中没有起到重要作用。然而，在计算机上表达分析显示，鉴定出的逆转录转座子的个别结构域在雄性植物中表达存在偏倚。
我们对雌雄异株植物石竹属植物的 X 和 Y 染色体上的性连锁基因 AP3 的结构和进化进行了描述。这些拷贝表现出与常染色体直系同源物互补的表达模式和蛋白质水平上的进化松弛，这表明它们发生了亚功能化。Y 连锁等位基因的一个内含子被逆转录转座子入侵，这些转座子显示出与相应等位基因相似的性别特异性表达模式，这表明这些可移动元件可能影响了 Y 拷贝表达模式的进化。这些数据可以帮助研究人员破译转座元件在性染色体进化过程中退化过程中的作用。
