Cloning and Functional Analysis of EgrZHD5, a ZF-HD Transcription Factor in Eucalyptus, Reveals Its Role in Flowering Time and Xylem Development in Arabidopsis

The ZF-HD gene family in plants plays a critical role in growth and development. Through transcriptome sequencing of Eucalyptus grandis, transitioning from primary to secondary growth, we identified a differentially expressed ZF-HD gene family member, EgrZHD5 (Eucgr.H00572). Cloning and sequence analysis revealed that EgrZHD5 contains conserved zinc finger and homeobox which was a typical characteristic of the ZF-HD family. Subcellular localization assays further showed that EgrZHD5 localizes to the nucleus. To explore its function, EgrZHD5 was overexpressed in Arabidopsis thaliana. Phenotypic analysis of transgenic Arabidopsis lines revealed enhanced primary root elongation. Additionally, compared with wild-type plants, EgrZHD5 overexpression lines exhibited early flowering, initiating bloom 6-10 days earlier. Gene expression analysis of AtFT, AtSOC1, and AtFLC in transgenic plants showed significantly increased expression levels. Furthermore, the transgenic lines displayed reduced plant height, thinner stems, and thicker xylem cell walls, primarily due to EgrZHD5 promoting early flowering through the FT pathway, which also influenced plant height and xylem thickening. This study preliminarily characterizes the function of EgrZHD5, providing a potential candidate gene for early flowering to shorten the breeding cycle of eucalyptus.