Progress on plant orphan genes.

Orphan genes are located in a special evolutionary branch and have no significant sequence similarity with any other identified genes. Orphan genes are prevalent in every species, comparative genomics analyses found that all sequenced species contained a portion of orphan genes, and the number of orphan genes obtained by distinct screening conditions is different. Orphan genes are often associated with various stress responses, species-specific evolution and substance metabolism regulation. However, most of the orphan genes have not been well annotated or even have no recognizable functional domains, which brings some difficulties to the functional characterization of orphan genes. Compared with conserved genes, there is less research on orphan genes, which leads to the possibility that the importance of orphan genes may be "unrewarded". In this review, we summarize the origin and evolution of orphan genes, plant orphan gene screening and functions, and analyse the existing challenges and future research priorities and solutions, which provide theoretical basis for the study of orphan gene function and action mechanisms.