Identification of <i>WUSCHEL</i>-related homeobox (<i>WOX</i>) gene family members and determination of their expression profiles during somatic embryogenesis in <i>Phoebe bournei</i>

Abstract

WUSCHEL-related homeobox (<italic>WOX</italic>) transcription factor (TF)-encoding genes play crucial roles during embryo development. The function of <italic>WOX</italic> genes in embryonic development has been thoroughly studied in <italic>Arabidopsis thaliana</italic>, but little is known about their function in woody species, especially <italic>Phoebe bournei</italic>, an endemic and endangered species in China. In the present study, a total of 15 <italic>WOX</italic> genes were identified in<italic> P. bournei</italic>, and phylogenetic analysis resulted in their assignment to three typical clades: an ancient clade, an intermediate clade, and a modern/WUS clade. The gene structure and sequence characteristics and the physicochemical properties of WOX proteins were also analyzed. Promoter prediction indicated that <italic>WOX</italic> genes are likely involved in plant growth and development and hormone responses. Subsequently, we evaluated the expression patterns of <italic>WOX</italic> genes in response to auxin (IAA), abscisic acid (ABA), and methyl jasmonate (MeJA) treatments. According to tissue-specific expression patterns, we screened nine <italic>WOX</italic> genes that were present in embryonic calli and that might participate in the somatic embryogenesis (SE) of <italic>P. bournei.</italic> Furthermore, the expression profiles of these nine <italic>WOX</italic> genes during three phases of embryogenic calli development and three phases of somatic embryo development, namely, spheroid embryogenesis, immature cotyledon-producing embryogenesis and mature cotyledon-producing embryogenesis, were monitored. Overall, we systematically analyzed the expression patterns of <italic>WOX</italic> genes in <italic>P. bournei</italic> during SE, the information of which provides a basis for further elucidating the molecular mechanism through which <italic>WOX</italic> TFs function in <italic>P. bournei</italic> embryo development.