背景回顾：Azalea belongs to Rhododendron, which is one of the largest genera of flowering plants and is well known for the diversity and beauty in its more than 1,000 woody species.

提出问题：Rhododendron contains two distinct groups: the most high-altitude and a few low-altitude species, however, the former group is difficult to be domesticated for urban landscaping and their evolution and adaptation are little known.

研究对象：Rhododendron ovatum has broad adaptation in low-altitude regions but possesses evergreen characteristics like high-altitude species, and it has floral fragrance that deficient in most cultivars. 

主要研究：Here we report the chromosome-level genome assembly of R. ovatum, which has a total length of 549 Mb with scaffold N50 of 41 Mb and contains 41,264 predicted genes. 

结果1-低纬度适应性：Genomic micro-evolutionary analysis of R. ovatum in comparison with two high-altitude Rhododendron species indicated that the expansion genes in R. ovatum were significantly enriched in defense responses, which may account for its adaptability in low altitudes. 

结果2-TPS与花香：The R. ovatum genome contains much more terpene synthase genes (TPSs) compared with the species that lost floral fragrance. The subfamily b members of TPS are involved in the synthesis of sesquiterpenes as well as monoterpenes and play a major role in flora scent biosynthesis and defense responses. 

结果3-演化驱动力：Tandem duplication is the primary force driving expansion of defense responsive genes for extensive adaptability to the low-altitude environments. 

结论：The R. ovatum genome provides insights into low-altitude adaptation and gain or loss of floral fragrance for Rhododendron species, which are valuable for alpine plant domestication and floral scent breeding.

 摘 要 

杜鹃属（Rhododendron）是有花植物中含有植物物种最丰富的属之一，因其包含超过1000多种木本植物、具有丰富的物种多样性和极具观赏价值而闻名天下。杜鹃属植物可分成两大类，绝大部分属于高海拔地区，而少部分分布在低海拔地区，但高海拔地区的杜鹃很难被驯化，用于城市景观，并且其演化和适应性机制还不甚清楚。马银花（Rhododendron ovatum）在低海拔地区适应性广，但与高海拔品种一样具有常绿特性，并且具有大多数杜鹃栽培种所缺乏的花香。本文中，作者报道了马银花的基因组，全长549Mb，sacffold N50长为41Mb，共注释到41264个蛋白编码基因。通过比较马银花与另外两个高海拔地区的杜鹃物种基因组，作者发现马银花基因组中发生扩张的基因显著富集了与防御响应相关的条目，这可能与其适应低海拔环境相关。与失去花香的植物物种相比，马银花基因组中含有更多的萜类合酶基因（TPS）。TPS b亚家族成员参与倍半萜和单萜的合成，在植物花香化合物的生物合成和防御响应中发挥重要作用。作者发现串联复制是驱动防御响应相关基因扩展的主要动力，从而作用于马银花更好地适应低海拔环境。本文所报道的马银花基因组为杜鹃属植物的低海拔适应和花香的获得或丧失提供了新的见解，并且对于高山植物驯化和花香育种来说具有非常重要的价值。