Functional Analysis Of PtCDD And PtSZF Genes Involved In Development Of Secondary Vascular System In Poplar

Wood formation is a complex process composing many biological events. Programmed cell death (PCD) is the active process of cell death which occurs during secondary vascular system (SVS) development in response to environmental cues. Ca2+ dependent DNase from Populus tomentosa (PtCDD) play a critical role in PCD during the development of secondary vascular system in woody plants. To find out possible factors which interacts with PtCDD, we prepared cDNA from the cambial zone and subsequently amplified the full length of PtCDD and construct a cDNA yeast library to perform yeast two-hybridization analysis. We have screened the potential interacting factors of PtCDD in poplar cDNA library from cambium zone and finally got two potential targets named AD1-10, AD12-2. After sequencing and BLAST in GenBank, AD1-10 has been identified as a homolog of small subunit ribosomal RNA (mtSSU) gene, while AD12-2 is a function-unknown EST, induced by drought stress. The interaction between PtCDD and AD1-10 is verified in vitro by Pierce Lightshift EMSA, suggesting PtCDD likely participate in regulation of mitochondrion-mediated PCD of secondary vascular regeneration in woody plants.The function of zinc-finger protein PtSZF involved in SVS development needs further study. We have cloned the full-length cDNA of PtSZF gene from poplar through blasting protein sequence of PtSZF in Swiss-Model and EMBL-EBI online, and shown that PtSZF is a homology of CO(constans), a critical switch in light signaling-mediated flowering process. We made PtSZF overexpression construct, and transformed it into tobacco. The transgenic tobacco displayed several significant phenotypic changes when compared with wild type: thicker stem and delayed-flowering; Dramatic decrease of pith cells in number; Shorter Internode; extremely overexpressed (40-fold) line gave short and continual tilleringand failed to reproductive transition, suggesting that PtSZF might participate in many stages of tobacco development and regulate its overall growth cycle. It is significant to reveal the distinct function between PtSZF and its homolog in Arabidopsis and Oryza, which suggests that CO family genes likely play more ubiquitous and versatile roles in developmental process of woody plants except flowering control.