Expression dynamics of WOX homeodomain transcription factors during somatic embryogenesis in <i>Liriodendron</i> hybrids
Xiaofei Long, Jiaji Zhang, Dandan Wang, Yuhao Weng, Siqin Liu, Meiping Li, Zhaodong Hao, Tielong Cheng, Jisen Shi, Jinhui Chen
Abstract
The relict woody plant genus <italic>Liriodendron</italic> contains two endangered species, <italic>Liriodendron chinense</italic> and <italic>Liriodendron tulipifera</italic>. Understanding the molecular mechanisms involved in early embryo development is important for horticultural and ecological research, particularly for the development of improved somatic embryogenesis systems. However, the specific molecular processes underlying embryogenesis in these species remain largely unexplored. To address this, we investigated expression of the <italic>WOX</italic> (<italic>WUSCHEL-related homeobox</italic>) gene family of transcription factors throughout somatic embryogenesis. We confirmed expression of eight out of 11 novel candidate <italic>LcWOX</italic> genes in <italic>L.chinense</italic> using qRT-PCR and examined spatiotemporal expression patterns of the expressed genes using stable reporter lines that had been transformed with different <italic>LcWOX</italic> promoters driving GUS expression. We observed embryo developmental stages and expression patterns that broadly correlated with those reported for <italic>Arabidopsis</italic> somatic embryogenesis. <italic>LcWUS</italic> was weakly expressed during the transition stage and was predominantly restricted to the apical meristem. <italic>LcWOX5</italic> was specifically expressed in the root meristem and restricted to the cotyledons thereafter, and <italic>LcWOX4</italic> expression was restricted to the vascular tissue of cotyledonary embryos. In contrast, <italic>LcWOX9</italic> was expressed in the embryonic callus and the entire embryonic cell mass, then became restricted to the basal cells, indicating a potential role in regulating embryonic maintenance. Our findings provide insights into spatiotemporally specific <italic>WOX</italic> transcription and shed new light on potential functions of <italic>WOX</italic> genes during <italic>Liriodendron</italic> somatic embryogenesis.