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Doctoral thesis, 2016

Novel insights into vacuole-mediated control of plant growth and immunity

Liu, Qinsong

Abstract

Plant vacuoles are organelles with numerous biological functions in growth, development, and stress responses. These include maintenance of turgor pressure, storage of minerals and proteins, and degradation of cellular content delivered by endosomal trafficking and autophagy pathways. Intriguingly, vacuolar and autophagic processes have been implicated in hormone signaling during growth and immune responses, and in the regulation of programmed cell death (PCD). However, the molecular players and mechanisms underlying the vacuole-mediated control of growth and immunity remain poorly understood, and this thesis therefore aimed at improving our understanding of these systems. For this purpose, previously isolated lazarus (laz) suppressors of constitutive cell death in the Arabidopsis mutant accelerated cell death 11 (acd11) were characterized. LAZ4 encodes the retromer component VACUOLAR PROTEIN SORTING 35B (VPS35B). VPS35 proteins were found to contribute to certain forms of immunity-related cell death and disease resistance. Furthermore, retromer-dependent vacuole trafficking and integrity were shown to be essential for autophagy processes under basal and immunity-associated conditions. Another LAZ suppressor, LAZ1, and its closest homolog LAZ1H1 encode DUF300 domain-containing proteins and were found to localize to the tonoplast. Combined loss-of-function mutations in LAZ1 and LAZ1H1 resulted in altered vacuole morphology, growth inhibition, and constitutive activation of brassinosteroid (BR) hormone signaling. Vacuolar trafficking and degradation of the BR receptor BRI1 were shown to be enhanced in the laz1 laz1h1 mutant and associated with increased tonoplast accumulation of the BRI1 co-receptor BAK1. Since unrelated vacuole mutants exhibited normal BR responses, tonoplast DUF300 proteins were suggested to play distinct roles in the regulation of BR signaling. In addition, laz1 laz1h1 plants were impaired in basal autophagy. Since the laz1 single mutant showed a similar autophagic defect upon starvation and immunity-related PCD, LAZ1 was proposed to be the main contributor to autophagy function. Finally, the impact of enhanced autophagy on plant productivity and stress tolerance was analyzed. Constitutive overexpression of the autophagy-related genes ATG5 or ATG7 in Arabidopsis was shown to stimulate autophagy flux, which promoted immunity-related cell death and enhanced resistance to oxidative stress and necrotrophic fungal pathogens. Furthermore, increased autophagy improved vegetative growth and increased seed production. Therefore, genetic enhancement of autophagy levels could be potentially used in plants to improve various agronomically important traits.

Keywords

Arabidopsis; vacuole; retromer; DUF300 proteins; autophagy

Published in

Acta Universitatis Agriculturae Sueciae
2016, number: 2016:71
ISBN: 978-91-576-8644-2, eISBN: 978-91-576-8645-9
Publisher: Department of Plant Biology, Swedish University of Agricultural Sciences

Authors' information

Liu, Qinsong
Swedish University of Agricultural Sciences, Department of Plant Biology

UKÄ Subject classification

Other Biological Topics

URI (permanent link to this page)

https://res.slu.se/id/publ/77096