ASYMMETRIC LEAVES2-LIKE19/LATERAL ORGAN BOUNDARIES DOMAIN30 and ASL20/LBD18 regulate tracheary element differentiation in Arabidopsis.
ASYMMETRIC LEAVES2 (AS2)/LATERAL ORGAN BOUNDARIES DOMAIN (LBD) family proteins are plant-specific nuclear proteins, and genes encoding several family members have been implicated in plant development. We investigated the function of two members of the Arabidopsis thaliana AS2/LBD family, AS2-LIKE19 (ASL19)/LBD30 and ASL20/LBD18, which encode homologous proteins. Both ASL19 and ASL20 were expressed in immature tracheary elements (TEs), and the expression was dependent on VASCULAR-RELATED NAC-DOMAIN PROTEIN6 (VND6) and VND7, which are transcription factors required for TE differentiation. Overexpression of ASL19 and ASL20 induced transdifferentiation of cells from nonvascular tissues into TE-like cells, similar to those induced upon VND6/7 overexpression. By contrast, aberrant TEs were formed when a cDNA encoding a fusion protein of ASL20 with an artificial repressor domain (ASL20-SRDX) was expressed from its native promoter. These results provide evidence that ASL proteins positively regulate TE differentiation. In transgenic plants overexpressing both ASL19 and ASL20, the xylem-deficient phenotype caused by the expression of dominant-negative versions of VND6/7 proteins was not rescued. However, ectopic expression of VND7 was detected in plants overexpressing ASL20. Moreover, VND genes and their downstream targets were downregulated in ASL20-SRDX plants. Therefore, ASL20 appears to be involved in a positive feedback loop for VND7 expression that regulates TE differentiation-related genes.
Soyano
Takashi
T
Laboratory of Plant Molecular Biology, The Rockefeller University, New York, New York 10065, USA.
Thitamadee
Siripong
S
Machida
Yasunori
Y
Chua
Nam-Hai
NH
D017360:Arabidopsis / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology*; D008853:Microscopy; D030821:Plants, Genetically Modified / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D052584:Xylem / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; D011993:Recombinant Fusion Proteins