Cissus quadrangularis is a tetraploid species belonging to the Vitaceae family and is known for the Crassulacean acid metabolism (CAM) pathway in the succulent stem, while the leaves perform C3 photosynthesis. Here, we report a high-quality genome of C. quadrangularis comprising a total size of 679.2Mb which was phased into two subgenomes. Genome annotation identified 51,857 protein-coding genes, while approximately 47.75% of the genome was composed of repetitive sequences. Gene expression ratios of two subgenomes demonstrated that the sub-A genome as the dominant subgenome played the vital role during the drought tolerance. Genome divergence analysis suggests that the tetraploidization event occurred around 8.9 million years ago. Transcriptome data revealed that pathways related to cutin, suberine, and wax metabolism were enriched in the stem during drought treatment, suggesting that these genes contributed to the drought adaption. Additionally, a subset of CAM-related genes displayed diurnal expression patterns in the succulent stems but not in leaves, indicating that stem-biased expression of existing genes contributed to the CAM evolution. Our findings provide insights into the mechanisms of drought adaptation and photosynthesis transition in plants.

中文翻译：

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白粉藤基因组揭示了其在干旱栖息地的适应性特征

Cissus fourrangleis 是属于葡萄科的四倍体物种，以肉质茎中的景天酸代谢 (CAM) 途径而闻名，而叶子则进行 C3 光合作用。在这里，我们报告了一个高质量的四边形角藻基因组，总大小为 679.2Mb，分为两个亚基因组。基因组注释识别出 51,857 个蛋白质编码基因，而大约 47.75% 的基因组由重复序列组成。两个亚基因组的基因表达比表明，亚A基因组作为优势亚基因组在耐旱过程中发挥着至关重要的作用。基因组分歧分析表明四倍体化事件发生在大约 890 万年前。转录组数据显示，在干旱处理期间，与角质、木栓质和蜡质代谢相关的途径在茎中富集，表明这些基因有助于干旱适应。此外，CAM 相关基因的一个子集在肉质茎中显示出昼夜表达模式，但在叶子中却没有，这表明现有基因的茎偏向表达有助于 CAM 进化。我们的研究结果为植物适应干旱和光合作用转变的机制提供了见解。