附生和内生是绿藻的两种特殊生存方式。其中，附生于高等植物表皮的绿藻较为常见，而内生于高等植物体内的现象极为罕见。项目组在前期研究中发现两个绿藻新种，一个附生于树皮表面，命名为王棕橡藻，另一个内生于橡胶树体内，命名为海南橡藻，两者同属一个绿藻新属——橡藻属（Heveochlorella）。两个近缘种显微、超微结构及发育方式相似，但自养条件下附生的王棕橡藻生长快，而内生的海南橡藻几乎不长，光合作用微弱；在补充碳源情况下内生藻会大量积累油脂，含量远高于附生藻。说明两者碳流在源与库两端都存在显著差异，其机制尚不清楚。本项目拟用生理生化和比较转录组学方法系统研究两者在光合作用和油脂积累方面的差异，构建绿藻光合作用和油脂代谢的转录调控网络，挖掘导致内生藻光合作用衰退和油脂积累能力增强的关键基因，解析橡藻属从附生到内生进化过程中的适应性演变，为探讨内生藻类与高等植物协同进化的机制奠定基础。

Epiphyte and endophyte are two special life styles of green algae. Epiphytic green algae are widely seen on higher plants’ surface. However, endophytic algae are rare in higher plants. In previous studies, we identified two novel algal species, in which Heveochlorella roystonensis is an epiphytic, and Heveochlorella hainangensis is an endophytic alga dwelling in rubber tree, and they belong to the same genus. These two species are morphologically similar with similar chloroplasts and developmental pattern. However, during autotrophic growth, the epiphytic strain grew well, but the endophytic strain grew badly with almost no growth and no photosynthesis. When they were supplied with carbon source, the endophytic strain accumulated large amount of oil, a content much higher compared to that of the epiphytic strain. These results indicated that the two strains are significantly different in both the source and basin of carbon flow. The mechanism related to these differences are unknow. In this proposal, we propose to systematically analyze the differences in photosynthesis and oil biosynthesis between these two species using physiological and biochemistry methods, as well as comparative transcriptome analysis, and construct the regulation networks of photosynthesis and oil biosynthesis, and discover the key regulating genes that result in photosynthesis failure and oil accumulation-active properties of Heveochlorella hainangensis. These researches will uncover the mechanism of adaptability changes of microalgae from the epiphytic life style to the endophytic life style, and the mechanism of co-evolution between microalgae and higher plants.