**Jiadai He 1,**†**, Hua Zhao 1,**†**, Zhilu Cheng 2, Yuwei Ke 3, Jiaxi Liu <sup>1</sup> and Haoli Ma 1,\***


Received: 22 February 2019; Accepted: 19 April 2019; Published: 20 April 2019

**Abstract:** The fasciclin-like arabinogalactan proteins (FLAs) play important roles in plant development and adaptation to the environment. FLAs contain both fasciclin domains and arabinogalactan protein (AGP) regions, which have been identified in several plants. The evolutionary history of this gene family in plants is still undiscovered. In this study, we identified the *FLA* gene family in 13 plant species covering major lineages of plants using bioinformatics methods. A total of 246 *FLA* genes are identified with gene copy numbers ranging from one (*Chondrus crispus*) to 49 (*Populus trichocarpa*). These FLAs are classified into seven groups, mainly based on the phylogenetic analysis of plant FLAs. All FLAs in land plants contain one or two fasciclin domains, while in algae, several FLAs contain four or six fasciclin domains. It has been proposed that there was a divergence event, represented by the reduced number of fasciclin domains from algae to land plants in evolutionary history. Furthermore, introns in *FLA* genes are lost during plant evolution, especially from green algae to land plants. Moreover, it is found that gene duplication events, including segmental and tandem duplications are essential for the expansion of *FLA* gene families. The duplicated gene pairs in *FLA* gene family mainly evolve under purifying selection. Our findings give insight into the origin and expansion of the *FLA* gene family and help us understand their functions during the process of evolution.

**Keywords:** fasciclin-like AGP; FLA; evolution; phylogeny
