Towards understanding of plasmodesmal regulators
Date
2015
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Arabidopsis Casein Kinase I-like 6 (CKL6), a homolog of tobacco PAPK1 (plasmodesmal-associated protein kinase 1), localizes to plasmodesmata (PD) and associates with both microtubules and actin filaments. To study the distinctive localization pattern of CKL6, EMS-induced mutagenesis was carried out on plants overexpressing CKL6-DsRed2 and one group of mutants with condensed CKL6-carrying vesicles was isolated. One mutant line, CKL6 effector mutant 1-1 (cem1-1 ), was chosen for map-based cloning and rough mapping located the mutation between 6.4 and 12.9 Mb on Chromosome 2. Fine mapping revealed that cem1-1 carries a novel missense mutation in gene At2G20370, previously identified as KATAMARI1/MURUS3 (KAM1/MUR3 ). KAM1/MUR3 is a transmembrane protein containing an exostosin domain and localizes to the Golgi apparatus. Complementation assay confirmed that the missense mutation in KAM1/MUR3 caused the vesicle-condensation phenotype in cem1-1, whereas allele test suggested that an additional mutation closely linked to KAM1/MUR3 caused the early-bolting phenotype in cem1-1. A model was proposed, in which CKL6 facilitates its own transport along cytoskeleton and the process is retarded in cem1-1. Callose dynamics at PD plays an active role in regulating PD permeability, but the upstream signaling pathway is still unclear. Arabidopsis PD-localized protein 5 (PDLP5), a transmembrane protein localizing to PD, positively regulates basal and salicylic acid (SA)-induced PD callose deposition. To seek out the executive protein of PDLP5, potentially a PD-specific callose synthase (CalS), a series of cals mutants were screened for altered PD callose level under basal and SA-induced conditions. Three members stood out: CalS8 and CalS10 regulate basal PD callose deposition and PD permeability, while CalS1 regulates SA-induced PD callose deposition and PD closure. Examination of various crossed lines revealed that both CalS8 and CalS1 are downstream executive proteins of PDLP5, whereas CalS10 functions independently of the PDLP5 pathway. Further investigation revealed that CalS8 is also responsible for wound- and H 2 O2 -induced PD callose deposition and PD closure in a manner independent of PDLP5. Additionally, CalS8 is required for plant basal immunity against virulent bacteria. A model was proposed to explain different signaling pathways leading to PD callose deposition. Future research will focus on the subcellular localization of these CalS and their roles in plant development and immunity.