An Allelic Series of bak1 Mutations Differentially Alter bir1 Cell Death, Immune Response, Growth, and Root Development Phenotypes in Arabidopsis thaliana

Abstract

Receptor-like kinases (RLKs) mediate cell-signaling pathways in Arabidopsis thaliana, including those controlling growth and development, immune response, and cell death. The RLK coreceptor BRI1-ASSOCIATED KINASE-1 (BAK1) partners with multiple ligand-binding RLKs and contributes to their signaling in diverse pathways. An additional RLK, BAK1-INTERACTING RECEPTOR-1 (BIR1), physically interacts with BAK1, and loss-of-function mutations in BIR1 display constitutive activation of cell death and immune response pathways and dwarfism and a reduction in lateral root number. Here we show that bir1 plants display defects in primary root growth, characterize bir1 lateral root defects, and analyze expression of BIR1 and BAK1 promoters within the root. Using an allelic series of bak1 mutations, we show that loss of BAK1 function in immune response pathways can partially suppress bir1 cell death, immune response, and lateral root phenotypes and that null bak1 alleles enhance bir1 primary root phenotypes. Based on our data, we propose a model in which BIR1 functions to regulate BAK1 participation in multiple pathways.KEYWORDS receptor-like kinases; genetic suppression; cell death; lateral roots R ECEPTOR-like kinases (RLKs) are a major component of signaling pathways in plants. Composed of an extracellular domain, single-pass transmembrane region, and a cytoplasmic kinase domain, RLKs share structural similarity with the animal receptor tyrosine kinases (RTKs) yet share sequence similarity with the Toll-like receptors (TLRs) and their associated kinases Bleecker 2001a, Asai et al. 2002). The RLK family is greatly expanded in plants compared to RTK and TLR families, with over 600 RLKs in Arabidopsis as opposed to 58 RTKs and 13 TLRs in humans (Nurnberger et al. 2004). This may reflect an increased need for receptor-mediated signaling in plants owing to their sessile nature and lack of cell motility, as well as their sole reliance on an innate immune system for pathogen recognition [reviewed in Nurnberger et al. (2004)].RLKs in Arabidopsis are essential components of signaling pathways in diverse processes from growth and development to the recognition of conserved pathogen-associated molecular patterns (PAMPs) in pathogen-triggered immunity (PTI) [reviewed in Schwessinger and Ronald (2012) and Shiu and Bleecker (2001b)]. Perhaps the most wellcharacterized RLK-mediated pathway is the pathway containing BRASSINOSTEROID INSENSITIVE 1 (BRI1), a leucine-rich repeat domain containing RLK (LRR-RLK), which serves as the major ligand-binding receptor for the plant steroid hormone brassinosteroid (BR). BR signaling functions to promote both cell division and cell expansion and influences many processes in plants, including germination, vascular differentiation, vegetative and reproductive growth, root growth and gravitropism, photomorphogenesis, flowering time, biotic and abiotic stress response, and male fertility [reviewed in Zhu et al. (2013)].Within PTI signaling, LRR-RLK-mediated pathways trigger transcriptional chang...

False idolatry of the mythical growth versus immunity tradeoff in molecular systems plant pathology

“…This is being driven by molecular studies that are finding interactions between regulatory genes involved in the control of growth and defense. These links are being found in related signaling pathways that interlink the brassinosteroid and effector triggered immunity pathways [7,11,12,15]. Similar links between development and plant defense signaling have been found for gibberellins, salicylic acid, auxin and jasmonic acid [16e22].…”

Two Ubiquitin-Activating Systems Occur in Plants with One Playing a Major Role in Plant Immunity

“…To test FLS2 and EFR-mediated immunity in Arabidopsis ubc32 , ubc33 , and ubc34 single, double and triple mutant lines, seedling growth inhibition assay was performed as described (Wierzba and Tax, 2016). Specifically, Arabidopsis seeds were sterilized and then sowed on ½ MS (Murashige and Skoog) agar plates for stratification for 3 days, followed by moving the plates to short day conditions (22 °C, 10 h light, and 65-70% relative humidity) for germination for 3 days.…”

QTL Verification and Candidate Gene Screening of Fiber Quality and Lint Percentage in the Secondary Segregating Population of Gossypium hirsutum

“…GH_A07G2222 in the interval of the QTL cluster on chromosome 7 was annotated possibly as BRASSINOSTEROID-INSENSITIVE1 (BRI1)-associated kinase 1 (BAK1)-interacting receptor-like kinase 1 (BIR1), a small leucine-rich repeat receptor-like kinase. In Arabidopsis, BIR1 was demonstrated to negatively regulate cell death pathways in plant BAK1-mediated pathogen-triggered immunity (PTI) signaling [52,53]. The functioning of BIR1 is partially dependent on the salicylate (SA)-dependent resistance (R) protein pathway [54].…”