Vacuole Integrity Maintained by DUF300 Proteins Is Required for Brassinosteroid Signaling Regulation

• Published in: Molecular plant 2018-04, Vol.11 (4), p.553-567
• Main Authors: Liu, Qinsong, Vain, Thomas, Viotti, Corrado, Doyle, Siamsa M., Tarkowská, Danuše, Novák, Ondřej, Zipfel, Cyril, Sitbon, Folke, Robert, Stéphanie, Hofius, Daniel
• Format: Article
• Language: English
• Subjects: Apoptosis Regulatory Proteins - genetics; Apoptosis Regulatory Proteins - metabolism; Arabidopsis; Arabidopsis - cytology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Biochemistry and Molecular Biology; Biokemi och molekylärbiologi; brassinosteroid signaling; Brassinosteroids - metabolism; Cell Biology; Cellbiologi; Developmental Biology; DUF300 proteins; Mutation; Protein Transport; Signal Transduction; tonoplast; Utvecklingsbiologi; vacuole integrity; Vacuoles - metabolism
• ISSN: 1674-2052; 1752-9867; 1752-9867
• DOI: 10.1016/j.molp.2017.12.015

Brassinosteroid (BR) hormone signaling controls multiple processes during plant growth and development and is initiated at the plasma membrane through the receptor kinase BRASSINOSTEROID INSENSITIVE1 (BRI1) together with co-receptors such as BRI1-ASSOCIATED RECEPTOR KINASE1 (BAK1). BRI1 abundance is regulated by endosomal recycling and vacuolar targeting, but the role of vacuole-related proteins in BR receptor dynamics and BR responses remains elusive. Here, we show that the absence of two DUF300 domain-containing tonoplast proteins, LAZARUS1 (LAZ1) and LAZ1 HOMOLOG1 (LAZ1H1), causes vacuole morphology defects, growth inhibition, and constitutive activation of BR signaling. Intriguingly, tonoplast accumulation of BAK1 was substantially increased and appeared causally linked to enhanced BRI1 trafficking and degradation in laz1 laz1h1 plants. Since unrelated vacuole mutants exhibited normal BR responses, our findings indicate that DUF300 proteins play distinct roles in the regulation of BR signaling by maintaining vacuole integrity required to balance subcellular BAK1 pools and BR receptor distribution. Hormone signaling by growth-promoting brassinosteroids (BR) is initiated at the plasma membrane (PM) through the receptor kinase BRASSINOSTEROID INSENSITIVE1 (BRI1) and co-receptors such as BRI1-ASSOCIATED RECEPTOR KINASE1 (BAK1). BR receptor abundance at the PM is regulated by endosomal recycling and vacuolar targeting of BRI1, but it remained largely unknown if and how vacuolar functions and tonoplast-resident proteins influence BRI1 trafficking and BR responses. Our loss-of-function analysis of the two closely related DUF300 proteins LAZ1 and LAZ1H1 provides evidence for a critical role of vacuole membrane integrity in BR signaling, and identifies tonoplast pools of BAK1 as an important factor in the control of BRI1 receptor activation and distribution.