Is auxin involved in the induction of genetic instability in barley homeotic double mutants?

Abstract

The triggers of genetic instability in barley homeotic double mutants are tweaky spike -type mutations associated with an auxin imbalance in separate spike phytomeres. Barley homeotic tweaky spike;Hooded (tw;Hd) double mutants are characterized by an inherited instability of spike and flower development, which is absent in the single parental constituents. The aim of the present study was to show that the trigger of genetic instability in the double mutants is the tw mutations, which are associated with an auxin imbalance in the developing spikes. Their pleiotropic effects on genes related to spike/flower development may cause the genetic instability of double mutants. The study of four double-mutant groups composed of different mutant alleles showed that the instability arose only if the mutant allele tw was a constituent of the double mutants. Application of auxin inhibitors and 2,4-dichlorophenoxyacetic acid (2,4-D) demonstrated the relationship of the instability of the double mutants and the phenotype of the tw mutants to auxin imbalance. 2,4-D induced phenocopies of the tw mutation in wild-type plants and rescued the phenotypes of three allelic tw mutants. The differential display (dd-PCR) method allowed the identification of several putative candidate genes in tw that may be responsible for the initiation of instability in the double mutants by pleiotropic variations of their expression in the tw mutant associated with auxin imbalance in the developing spikes. The results of the present study linked the genetic instability of homeotic double mutants with an auxin imbalance caused by one of the constituents (tw). The genetic instability of the double mutants in relation to auxin imbalance was studied for the first time. A matrocliny on instability expression was also observed.

Application of Barley Tweaky Spike Mutants for the Study of Effects of Plant Immunity-Related Substances

“…Depending on the years, the fraction of aberrant flowers of mutants tw, tw 1 , and tw 2 fluctuates in the ranges of 63-80%, 29-48% and 32-90% (respectively) [unpublished data], and such expressivity variations in flower structure from year to year can directly influence the quality of grains from different years. The present study revealed a smaller than expected effect of the exogenous synthetic auxin 2,4-D and both auxin inhibitors HFCA and PCIB on MGG frequency in tw-type mutants, considering their dramatic rescue effects on variations in spike and floral structure (respectively), which were revealed in our previous works [8,9]. Such a negligible effect of 2,4-D and both auxin inhibitors on MGG frequency of different tweaky-type mutants, strongly suggests that auxin pathway disturbances in tw-type mutants are generally restricted to the spike and floral structure but not to germination events.…”

“…For root length measurements, roots of 30 germinating grains were measured in total (i.e., 10 germinating grains per experimental replicate). The concentrations of the compounds were selected from small-scale experiments and our previous studies [8,9]. 2,4-D was manufactured by Alfa Aesar (Germany), and all the other compounds were obtained from Sigma-Aldrich (USA).…”

“…Our recent studies have related the tw phenotype to disrupted auxin physiology [8,9], providing a pretext to study the role of auxin in the MGG phenomenon. Depending on lifestyle, phytopathogens develop means for controlling plant growth by modulating endogenous auxin synthesis and signalling [10].…”