Figure 1.

The SNBE sequences are capable of driving the GUS reporter gene expression in secondary wall-forming cells. (A) The top part shows the representative SNBE sequences from the promoters of several SWN direct targets, including transcription factors (MYB46, MYB83, SND3, MYB103, KNAT7) and hydrolases involved in programmed cell death [a ribonuclease (RNS3) and a xylem-specific cysteine protease (XCP1)]. The critical nucleotides in the SNBE sequences are shaded. The lower part shows the tracheary element responsive elements (TERE) from two xylem-specific cysteine proteases (XCP1 and XCP2) together with the consensus TERE sequence. (B) Diagram of the GUS reporter gene driven by three copies of SNBE sequence from various SWN direct target promoters as shown in (A). The GUS reporter constructs in a binary vector were introduced into Arabidopsis and at least 30 transgenic plants in the first generation were examined for GUS expression. CaMV, cauliflower mosaic virus; NosT, nopaline synthase terminator. (C and D) Cross sections of stems from transgenic plants expressing the GUS reporter gene driven by five copies of XCP1-TERE (C) and XCP2-TERE (D) showing the absence of GUS staining. (E to J) Cross sections of stems from transgenic plants expressing the GUS reporter gene driven by three copies of representative SNBE sequence from MYB46 (E and F), MYB83 (G), SND3 (H), MYB103 (I) and KNAT7 (J) showing the GUS staining in secondary wall-forming cells, including xylem and interfascicular fibers. (K and L) Cross sections of stems from transgenic plants expressing the GUS reporter gene driven by 3 copies of SNBE sequence from RNS3 (K) and XCP1 (L) showing the specific GUS staining in the xylem. if, interfascicular fiber; xy, xylem. Scale bar in (C) = 125 µm for (C–L).