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Abstract
Vascular cambium, a type of lateral meristem, is the source of secondary xylem and secondary phloem, but little is known about the molecular mechanisms of its formation and development. Here, we report the characterization of an Arabidopsis thaliana gain-of-function mutant with dramatically increased cambial activity, designated high cambial activity2 (hca2). The hca2 mutant has no alternative organization of the vascular bundles/fibers in inflorescence stems, due to precocious formation of interfascicular cambium and its subsequent cell division. The phenotype results from elevated expression of HCA2, which encodes a nuclear-localized DNA binding with one finger (Dof) transcription factor Dof5.6. Dof5.6/HCA2 is preferentially expressed in the vasculature of all the organs, particularly in the cambium, phloem, and interfascicular parenchyma cells of inflorescence stems. Dominant-negative analysis further demonstrated that both ubiquitous and in situ repression of HCA2 activity led to disruption of interfascicular cambium formation and development in inflorescence stems. In-depth anatomical analysis showed that HCA2 promotes interfascicular cambium formation at a very early stage of inflorescence stem development. This report demonstrates that a transcription factor gene, HCA2, is involved in regulation of interfascicular cambium formation and vascular tissue development in Arabidopsis.
Highlights
Vascular tissues, either primary or secondary, of higher plants play essential roles in transport of water, nutrients, and signaling molecules and in physical support (Scarpella and Meijer, 2004; Sieburth and Deyholos, 2006)
In order to identify novel components involved in vascular cambium development in plants, we screened for altered vascular tissues in an Arabidopsis activation tagging mutant collection, which was generated using the activation tagging vector pSKI015 as described previously (Qin et al, 2003, 2005)
We provide evidence that a DNA binding with one finger (Dof) transcription factor gene Dof5.6/HCA2 plays an important role in the regulation of vascular tissue development
Summary
Either primary or secondary, of higher plants play essential roles in transport of water, nutrients, and signaling molecules and in physical support (Scarpella and Meijer, 2004; Sieburth and Deyholos, 2006). Vascular tissue development occurs in a highly ordered and predictable pattern. In plant stems, it involves the formation and regulation of cambium, which consists of fascicular cambium and interfascicular cambium (Lachaud et al, 1999; Helariutta, 2007). Fascicular cambium, initiated from procambium, is present in between the xylem and phloem of a vascular bundle (Larson, 1994). When the interfascicular cambia originated from two adjacent vascular bundles connect, a continuous ring of vascular cambium is established. A continuous ring of vascular cambium is characteristic of the secondary growth in stems of gymnosperms, woody dicots, and, to a limited extent, some herbaceous dicots (Esau, 1977; Mauseth, 1988)
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