Page 165 - PC2019 Program & Proceedings

PLANT CANADA 2019

S115. Hsp70 mediates programmed cell death during the remodeling of lace plant leaves
(Aponogeton madagascariensis)
*1
2
Rowarth, N. ; A. Dauphinee ; G. Denbigh ; A. Gunawardena
1
1
1 Dalhousie
2 Swedish University of Agricultural Sciences

Leaves of the lace plant utilize programmed cell death (PCD) to form perforations during development.
Heat shock proteins (Hsps) are essential for development and are known to be involved in plant PCD,
however, have not been investigated in lace plants. Hsp70 levels were analyzed throughout lace plant leaf
development and results indicate they are highest during early development before and during PCD. Basal
Hsp70 synthesis correlates with raised anthocyanin levels and caspase-like protease activity (CLP), two
hallmarks of lace plant PCD. We treated whole plants with known regulators of PCD (ROS and
antioxidants) alongside an Hsp70 inhibitor, chlorophenylethynylsulfonamide (PES-Cl) to investigate the
effects of Hsp70 on leaf development. ROS induced Hsp70 2-fold and CLP in early developing leaves,
however, there was no change in anthocyanin levels and the number of perforations formed. Antioxidants
significantly decreased Hsp70 and CLP in early leaves, resulting in significantly less anthocyanin and the
fewest perforations. PES-Cl induced Hsp70 4-fold in early leaves, causing anthocyanin, superoxide and
CLP to significantly decline, leading to fewer perforations. The departure from basal Hsp70 levels in
young leaves alters anthocyanin and CLP, inhibiting PCD induction. Our results indicate Hsp70 plays a
role in lace plant leaf development by mediating PCD.

Nathan Rowarth (nathan.rowarth@dal.ca)

S116. An Arabidopsis G-protein-coupled receptor-like module regulates cellulose synthase enzyme
secretion
McFarlane, H.
University of Toronto

Cellulose is crucial for plant morphology and water transport and also provides raw material for fibre and
fuel industries. Cellulose is produced at the plasma membrane by large Cellulose Synthase (CESA)
protein complexes. These CESA complexes must be secreted from the Golgi apparatus to reach the
plasma membrane; however, the regulatory framework for this secretion is not clear. We have identified
several members of the seven transmembrane domain containing protein (7TM) family as important for
cellulose production during cell wall integrity stress. Cell wall stress, such as cellulose synthesis
inhibition, resulted in reduced growth, cell swelling, and reduced cellulose production in the 7tm mutants
compared to wild-type. 7TM proteins are often associated with G-protein signaling. Indeed, mutants for
several of the canonical G-protein complex components were also hypersensitive to cell wall
stress. Furthermore, the 7TM proteins could interact with the G-protein complex at the Golgi apparatus
and trans-Golgi network. To understand the cellulose deficient phenotype of 7tm mutants, we examined
fluorescently tagged CESAs in the 7tm mutants. While the CESAs at the plasma membrane were
unaffected, CESA secretion was substantially reduced in mutant plants, compared to wild-type. By
contrast, other secreted proteins appeared unaffected. We propose a model in which G-protein coupled
7TM proteins regulate CESA trafficking and defects in this process result in hypersensitivity to cell wall
integrity stress.

Heather McFarlane (h.mcfarlane@utoronto.ca)

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