Reduced coenzyme Q synthesis confers non-target site resistance to the herbicide thaxtomin A.

Herbicide resistance in weeds is a growing threat to global crop production. Non-target site resistance is problematic because a single resistance allele can confer tolerance to many herbicides (cross resistance), and it is often a polygenic trait so it can be difficult to identify the molecular mechanisms involved. Most characterized molecular mechanisms of non-target site resistance are caused by gain-of-function mutations in genes from a few key gene families-the mechanisms of resistance caused by loss-of-function mutations remain unclear. In this study, we first show that the mechanism of non-target site resistance to the herbicide thaxtomin A conferred by loss-of-function of the gene PAM16 is conserved in Marchantia polymorpha, validating its use as a model species with which to study non-target site resistance. To identify mechanisms of non-target site resistance caused by loss-of-function mutations, we generated 107 UV-B mutagenized M. polymorpha spores and screened for resistance to the herbicide thaxtomin A. We isolated 13 thaxtomin A-resistant mutants and found that 3 mutants carried candidate resistance-conferring SNPs in the MpRTN4IP1L gene. Mprtn4ip1l mutants are defective in coenzyme Q biosynthesis and accumulate higher levels of reactive oxygen species (ROS) than wild-type plants. Mutants are weakly resistant to thaxtomin A and cross resistant to isoxaben, suggesting that loss of MpRTN4IP1L function confers non-target site resistance. Mutants are also defective in thaxtomin A metabolism. We conclude that loss of MpRTN4IP1L function is a novel mechanism of non-target site herbicide resistance and propose that other mutations that increase ROS levels or decrease thaxtomin A metabolism could contribute to thaxtomin A resistance in the field.

Psychometric Properties of the ICECAP-O Quality of Life Measurement Tool When Self-reported by Community-dwelling Older People With Mild and Moderate Dementia.

To evaluate interventions designed to improve the quality of life of people with dementia (PWD), there is a need for psychometrically validated instruments. We tested the psychometric properties of the ICEpop CAPability measure for Older people (ICECAP-O) as a self-report measure of quality of life with PWD. We used data from a randomized controlled trial of Tai Chi with 83 community-dwelling older people with mild and moderate dementia. The ICECAP-O was found to be valid with correlations in the expected directions for fear of falls (r=-0.36, P=0.001) and age (r=0.12, P=0.29), sensitive to change (mean difference=0.051, P=0.04, d=0.51), and have an adequate factorial structure. The ICECAP-O is a valid, generic measure of quality of life for use with PWD without a proxy.