Expression Analysis of Two NAC Transcription Factors PtNAC068 and PtNAC154 from Poplar

NAM/ATAF/CUC (NAC) family genes comprise one of the largest families of transcription factors in plant genomes and are widely expressed in developing woody tissues. In the present study, we constructed plant transformation vectors using the beta-glucuronidase (GUS) reporter gene system and detected the promoter expression patterns derived from the PtNAC068 and PtNAC154 genes of Chinese white poplar (Populus tomentosa Carr.) in transgenic poplars (Populus alba x Populus glandulosa). The results showed that the GUS expression driven by PtNAC068 and PtNAC154 promoters may be more complex in poplar than they are in Arabidopsis. Histochemical GUS assays showed that GUS activity driven by PtNAC068 promoter was mainly in vascular tissues of stems, leaves, petioles, and roots, while that driven by PtNAC154 promoter was confined to the developing secondary xylem of stems and veins of leaves. The transcript level of both PtNAC068 and PtNAC154 in successive internodes below the apex was found to be much higher in IN5-10 compared to that in IN2-4 as measured by real-time RT-PCR, suggesting that PtNAC068 and PtNAC154 upregulation is related to secondary growth in poplar. GUS expression in internodes 3-8 of ProNAC068::GUS transgenic plants was 30-fold higher than that in ProNAC154::GUS transgenic plants. The differences in the expression pattern and transcript level of mRNA accumulation indicate that PtNAC068 and PtNAC154 may be involved in two distinct aspects of vascular tissue development.