Chitinase-Like Protein CTL1 Plays a Role in Altering Root System Architecture in Response to Multiple Environmental Conditions      

Abstract

Plant root architecture is highly responsive to changes in nutrient availability. However, the molecular mechanisms governing the adaptability of root systems to changing environmental conditions is poorly understood. A screen for abnormal root architecture responses to high nitrate in the growth medium was carried out for a population of ethyl methanesulfonatemutagenized Arabidopsis (Arabidopsis thaliana). The growth and root architecture of the arm (for anion altered root morphology) mutant described here was similar to wild-type plants when grown on low to moderate nitrate concentrations, but on high nitrate, arm exhibited reduced primary root elongation, radial swelling, increased numbers of lateral roots, and increased root hair density when compared to the wild-type control. High concentrations of chloride and sucrose induced the same phenotype. In contrast, hypocotyl elongation in the dark was decreased independently of nitrate availability. Positional cloning identified a point mutation in the AtCTL1 gene that encodes a chitinase-related protein, although molecular and biochemical analysis showed that this protein does not possess chitinase enzymatic activity. CTL1 appears to play two roles in plant growth and development based on the constitutive effect of the arm mutation on primary root growth and its conditional impact on root architecture. We hypothesize that CTL1 plays a role in determining cell wall rigidity and that the activity is differentially regulated by pathways that are triggered by environmental conditions. Moreover, we show that mutants of some subunits of the cellulose synthase complex phenocopy the conditional effect on root architecture under nonpermissive conditions, suggesting they are also differentially regulated in response to a changing environment.

CHITINASE-LIKE1/POM-POM1 and Its Homolog CTL2 Are Glucan-Interacting Proteins Important for Cellulose Biosynthesis in Arabidopsis

“…Asterisks indicate significant changes in percentage of colocalization compared with control treatment (Student's t test; *P < 0.05; **P < 0.01). Even though important amino acids for catalytic activity appear to have been changed in the CTLs (Passarinho and de Vries, 2002;Hermans et al, 2010;Hossain et al, 2010), it is still possible that the proteins have retained catalytic activities. However, chitinase activity of recombinant CTL1 protein purified from Escherichia coli was tested in vitro with negative results (Zhong et al, 2002;Hermans et al, 2010).…”

“…However, the biological function of the CTLs remains elusive. Mutations in CTL1/POM1 cause abnormal root swelling, ethylene overproduction, reduced tolerance to abiotic stresses, and ectopic deposition of lignin in Arabidopsis (Hauser et al, 1995;Schneider et al, 1997;Reed et al, 1998;Cary et al, 2001;Zhong et al, 2002;Rogers et al, 2005;Kwon et al, 2007;Hermans et al, 2010). In addition, cell walls of ctl1/pom1 mutants have an infrared spectrum that closely resembles cellulose-deficient mutants (Mouille et al, 2003).…”

Dissecting the Role of CHITINASE-LIKE1 in Nitrate-Dependent Changes in Root Architecture

“…In a previous screen designed to identify Arabidopsis mutants impaired in the repression of LR elongation by high nitrate concentration, we identified the arm (for anion-related root morphology) mutant that is an allele of CHITINASE-LIKE1 (CTL1; Hermans et al, 2010). Our data showed that the absence of CTL1 modifies root architecture in response to high concentrations of nitrate, chloride, or Suc.…”

Diverse chitinases are invoked during the activity-dormancy transition in spruce

“…Pg_GQ0046_J03.1 further displayed no evidence of a CBD or CTE, and showed a low sequence identity when compared to the other white spruce sequences (Online Resource 7). This sequence showed the most similarity to the A. thaliana sequences encoding CHITINASE-LIKE 1 (CTL1) and CHITINASE-LIKE 2 (CTL2), which are designated class II chitinases, although they lack chitinase activity (Zhang et al 2004;Hermans et al 2010;Sánchez-Rodríguez et al 2012). Both AtCTL1 and AtCTL2 lack the highly conserved histidine-glutamic acid-threonine-threonine (HETT) motif within loop 1 that is essential for chitinase activity (Passarinho and de Vries 2002).…”