UVM Theses and Dissertations
Format:
Print
Author:
Larson, Emily R.
Dept./Program:
Cell and Molecular Biology Program
Year:
2013
Degree:
Ph. D.
Abstract:
Root hairs are extensions of root epidennal cells that exhibit polarized growth, where all new plasma membrane proteins and cell wall components are secreted to the apical tip of the root hair. The secretion and assembly of cell wall components is important for the growth and function of these cells. We are interested in the interactions between cell wall structural networks that support root hair growth and how the organization of these networks contributes to root hair cell function.
The proline-rich structural proteins, PRP1 and PRP3 are required for root hair growth as seen by the aberrant root hairs of the prp1 and prp3 mutants. To define other cell wall networks that interact with networks established by these PRPs, we crossed the prp1 and prp3 mutants with mutants defective in cell wall biosynthetic enzymes whose activities are required for root hair growth. We identified novel root hair phenotypes in the F1 generation from crosses between both of the PRP mutants and csld3-2, a loss-of-function mutant in the Cellulose Synthase-Like D family, predicted to produce a [Beta]-glucan cell wall polymer. The genetic interaction between the root hair cell wall PRPs and CSLD3 was unique and did not include CSLD2, a close family member of CSLD3 that is also required for root hair growth. This work defines required interactions between the networks formed by the root hair cell wall proteins PRP1 and PRP3 with the cell wall polymer dependent upon CSLD3 activity, or a polysaccharide network that includes the CSLD3 glycan. We present a model that suggests that these networks define a cell wall structure that supports cell shape and function.
To test this model, we investigated gene expression changes in roots of the prp3 mutant and identified the SNARE VTI13, whose expression is up regulated in roots of prp3 seedlings when compared to wild type. This indicates that VTI13 expression is sensitive to changes in root hair extracellular matrix structure. Other members of the VTI SNARE family have been shown to function in endocytic trafficking to the lytic and storage vacuoles. A GFP-VTI13 fusion protein localizes to the vacuolar membrane and Brefeldin A-sensitive compartments of the trans-Golgi network (TGN). VTI13 localization is required for the organization of the TGN and the loss of function vtil3 mutant has a root hair phenotype, evidence that VTI13 function in the vacuole and TGN are required for root hair growth.
Together this work provides new evidence for interacting partners for the PRPs within the root hair cell wall and describes the network interactions formed between PRP1 and PRP3 with the CSLD3 polymer for maintaining root hair growth and cell shape. Changes in root hair cell wall organization can affect cellular function at the level of gene expression. One such gene sensitive to cell wall structure is VTI13, a SNARE protein whose function in the vacuole and TGN is required for root hair development. Analysis of the prp3 vti13 double mutant supports a model for VTI1 function in establishing and/or maintaining cell wall metabolism in growing root hairs.
The proline-rich structural proteins, PRP1 and PRP3 are required for root hair growth as seen by the aberrant root hairs of the prp1 and prp3 mutants. To define other cell wall networks that interact with networks established by these PRPs, we crossed the prp1 and prp3 mutants with mutants defective in cell wall biosynthetic enzymes whose activities are required for root hair growth. We identified novel root hair phenotypes in the F1 generation from crosses between both of the PRP mutants and csld3-2, a loss-of-function mutant in the Cellulose Synthase-Like D family, predicted to produce a [Beta]-glucan cell wall polymer. The genetic interaction between the root hair cell wall PRPs and CSLD3 was unique and did not include CSLD2, a close family member of CSLD3 that is also required for root hair growth. This work defines required interactions between the networks formed by the root hair cell wall proteins PRP1 and PRP3 with the cell wall polymer dependent upon CSLD3 activity, or a polysaccharide network that includes the CSLD3 glycan. We present a model that suggests that these networks define a cell wall structure that supports cell shape and function.
To test this model, we investigated gene expression changes in roots of the prp3 mutant and identified the SNARE VTI13, whose expression is up regulated in roots of prp3 seedlings when compared to wild type. This indicates that VTI13 expression is sensitive to changes in root hair extracellular matrix structure. Other members of the VTI SNARE family have been shown to function in endocytic trafficking to the lytic and storage vacuoles. A GFP-VTI13 fusion protein localizes to the vacuolar membrane and Brefeldin A-sensitive compartments of the trans-Golgi network (TGN). VTI13 localization is required for the organization of the TGN and the loss of function vtil3 mutant has a root hair phenotype, evidence that VTI13 function in the vacuole and TGN are required for root hair growth.
Together this work provides new evidence for interacting partners for the PRPs within the root hair cell wall and describes the network interactions formed between PRP1 and PRP3 with the CSLD3 polymer for maintaining root hair growth and cell shape. Changes in root hair cell wall organization can affect cellular function at the level of gene expression. One such gene sensitive to cell wall structure is VTI13, a SNARE protein whose function in the vacuole and TGN is required for root hair development. Analysis of the prp3 vti13 double mutant supports a model for VTI1 function in establishing and/or maintaining cell wall metabolism in growing root hairs.