Symplastically transmitted signals regulate pattern formation during root development in Arabidopsis thaliana
Year: 2012
Type: dissertation
Abstract: The exchange of positional information largely determines the fate of plant cells during organ development. Plasmodesmata (PD) are membrane-lined channels that connect the plant cells and allow symplastic cell-to-cell movement of developmental regulators and other molecules. Currently, little is known about the role of symplastic signaling in plant morphogenesis. In this study, the Arabidopsis root was used to investigate molecular control of the pattern formation and to elucidate how symplastic signaling regulates root development. We identified four novel mutants, phb-7d, cals3-1d, -2d, and -3d (collectively referred as cals3-d) that display defective protoxylem development. Characterization of these mutants revealed that the protoxylem defects are a result of an altered regulatory pathway involving the transcription factor SHORT-ROOT (SHR). It has been shown that SHR moves from the stele into the endodermis and the quiescent centre (QC) where it regulates cell division of the endodermis/cortex initials and maintains the stem cell identity. We identified phb-7d as a novel gain-of-function allele of PHABULOSA (PHB), which is normally post-transcriptionally regulated by microRNA165/6 (miR165/6). phb-7d carries a point mutation which renders it insensitive to regulation through miR165/6 and results in a loss of protoxylem identity. We found that SHR is required in the endodermis to turn on the expression of MIR165/6, which in turn is essential for the formation of the proper concentration gradient of PHB in the stele. We demonstrated that bidirectional non-cell-autonomous actions of SHR and miR165/6 are essential for the regulation of PHB, and therefore, for the regulation of protoxylem development. The movement of SHR from the stele is impeded in cals3-d. We defined that the cals3-d mutations are in the CALLOSE SYNTHASE 3 (CALS3)/GLUCAN SYNTHASE-LIKE 12 (GSL12) gene, whose product participates in the biosynthesis of callose, β-1,3-glucan. The cals3-1d, -2d and -3d lead to amino acid changes in the predicted cytosolic chains of CALS3 resulting in an increased callose biosynthesis. In order to characterize the role of the cals3-d in cell-to-cell communication, we engineered a spatiotemporally controlled miss-expression system for cals3-d. Using this system, we demonstrated that the aperture of a PD is controlled by the callose biosynthesis at the surrounding cell wall domain. Moreover, we identified symplastically transmitted cell signaling events. Our study reveals that SHR and miR165 traffic via the PD. In addition, we show that the phloem-borne symplastically transported signals are essential for the root development. In conclusion, this work demonstrates the fundamental importance of symplastic connectivity for the regulation of root morphogenesis.
Source: Työväentutkimus Vuosikirja
Author: Anne Vatén
Language: English
Subfield: Plant Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2222283907