Abstract：Class Ⅲ Homeodomain Leucine Zipper (HD-Zip Ⅲ) protein is mainly involved in the regulation of vascular tissue formation, apical meristem differentiation, embryonic morphogenesis and the polarity establishment of the lateral organs. In this study, the HD-Zip Ⅲ genes of Chinese fir (Cunninghamia lanceolata) were cloned by RACE based on the transcriptomic sequencing. Bioinformatic characteristics of the cloned ClHDZs were analyzed using online service. To understand genic roles in wood formation of Chinese fir, the expression patterns were analyzed in different organs and tissues. The results showed that four HD-Zip Ⅲ genes in Chinese fir were cloned and named ClHDZ1, ClHDZ2, ClHDZ3 and ClHDZ4, respectively. The corresponding encoding proteins were composed of 857, 841, 851 and 842 amino acid residues, respectively. And they contained 4 conserved domains of HD(homeodomain), LZ(leucine zipper), START(steroidogenic acute regulatory protein-related lipid transfer domain), SAD (START adjacent domain) and MEKHLA(Met, Glu, Lys, His, Leu, Ala). Phylogenetic tree suggested that HD-Zip Ⅲ proteins from gymnosperm and angiosperm were clustered in different branches. ClHDZ1 and ClHDZ3 appeared early in the evolution of eukaryotes, and ClHDZ2 and ClHDZ4 were grouped into the C8-subclass of gymnosperms. Four ClHDZs were expressed at different levels among the organs, and the expression levels in roots were the lowest. ClHDZ1 was mainly expressed in coniferous leaves and ClHDZ4 was preferentially expressed in female cones. ClHDZ2 and ClHDZ3 presented the similar expression patterns and were predominantly expressed in the stem, and their expression levels increased as the lignification progressed. This suggested that these 2 genes might participate in xylem development of Chinese fir. Further quantitative PCR analysis showed that ClHDZ2 was mainly expressed in the phloem and xylem, and the corresponding values were 1.0 and 1.2 times higher than that of the cambium. The expression level of ClHDZ3 in xylem was more than 8 times that of phloem and cambium. These 2 genes exhibited different expression patterns in response to compression wood induction. ClHDZ2 was predominantly expressed in the opposite wood. And transcripts of ClHDZ3 showed the same pattern as lignin changes, which were most abundant in compression wood. It further suggested that ClHDZ2 and ClHDZ3 might involve in regulation of Chinese fir wood formation. The molecular biology of the HD-Zip III gene of Chinese fir has provided a new scientific basis for revealing the formation of Chinese fir wood and has laid a foundation for further study on the molecular mechanism of Chinese fir wood formation.
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