Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
State Key Laboratory of Plant Diversity and Specialty Crops, Beijing 100093, China.
Plant Physiol. 2023 Nov 22;193(4):2622-2639. doi: 10.1093/plphys/kiad451.
Common purslane (Portulaca oleracea) integrates both C4 and crassulacean acid metabolism (CAM) photosynthesis pathways and is a promising model plant to explore C4-CAM plasticity. Here, we report a high-quality chromosome-level genome of nicotinamide adenine dinucleotide (NAD)-malic enzyme (ME) subtype common purslane that provides evidence for 2 rounds of whole-genome duplication (WGD) with an ancient WGD (P-β) in the common ancestor to Portulacaceae and Cactaceae around 66.30 million years ago (Mya) and another (Po-α) specific to common purslane lineage around 7.74 Mya. A larger number of gene copies encoding key enzymes/transporters involved in C4 and CAM pathways were detected in common purslane than in related species. Phylogeny, conserved functional site, and collinearity analyses revealed that the Po-α WGD produced the phosphoenolpyruvate carboxylase-encoded gene copies used for photosynthesis in common purslane, while the P-β WGD event produced 2 ancestral genes of functionally differentiated (C4- and CAM-specific) beta carbonic anhydrases involved in the C4 + CAM pathways. Additionally, cis-element enrichment analysis in the promoters showed that CAM-specific genes have recruited both evening and midnight circadian elements as well as the Abscisic acid (ABA)-independent regulatory module mediated by ethylene-response factor cis-elements. Overall, this study provides insights into the origin and evolutionary process of C4 and CAM pathways in common purslane, as well as potential targets for engineering crops by integrating C4 or CAM metabolism.
马齿苋（Portulaca oleracea）整合了 C4 和景天酸代谢（CAM）光合作用途径，是探索 C4-CAM 可塑性的有前途的模式植物。在这里，我们报道了 NAD-苹果酸酶（ME）亚型马齿苋的高质量染色体水平基因组，该基因组为 6630 万年前（Mya）在马齿苋科和仙人掌科的共同祖先中发生的 2 轮全基因组复制（WGD）提供了证据，以及另一个（Po-α）在 7740 万年前特属于马齿苋谱系的 WGD。在马齿苋中检测到参与 C4 和 CAM 途径的关键酶/转运蛋白的基因拷贝数比相关物种多。系统发育、保守功能位点和共线性分析表明，Po-α WGD 产生了用于马齿苋光合作用的磷酸烯醇丙酮酸羧化酶编码基因拷贝，而 P-β WGD 事件产生了参与 C4+CAM 途径的功能分化（C4 和 CAM 特异性）β碳酸酐酶的 2 个祖先基因。此外，启动子中的顺式元件富集分析表明，CAM 特异性基因既募集了夜间和午夜的生物钟元件，也募集了由乙烯反应因子顺式元件介导的独立于脱落酸（ABA）的调节模块。总体而言，这项研究提供了关于马齿苋中 C4 和 CAM 途径的起源和进化过程的见解，并为通过整合 C4 或 CAM 代谢来工程作物提供了潜在的目标。
