Knockout of the HvCKX1 or HvCKX3 Gene in Barley (Hordeum vulgare L.) by RNA-Guided Cas9 Nuclease Affects the Regulation of Cytokinin Metabolism and Root Morphology

Barley is among four of the most important cereal crops with respect to global production. Increasing barley yields to desired levels can be achieved by the genetic manipulation of cytokinin content. Cytokinins are plant hormones that regulate many developmental processes and have a strong influence on grain yield. Cytokinin homeostasis is regulated by members of several multigene families. CKX genes encode the cytokinin oxidase/dehydrogenase enzyme, which catalyzes the irreversible degradation of cytokinin. Several recent studies have demonstrated that the RNAi-based silencing of CKX genes leads to increased grain yields in some crop species. To assess the possibility of increasing the grain yield of barley by knocking out CKX genes, we used an RNA-guided Cas9 system to generate ckx1 and ckx3 mutant lines with knockout mutations in the HvCKX1 and HvCKX3 genes, respectively. Homozygous, transgene-free mutant lines were subsequently selected and analyzed. A significant decrease in CKX enzyme activity was observed in the spikes of the ckx1 lines, while in the ckx3 lines, the activity remained at a similar level to that in the control plants. Despite these differences, no changes in grain yield were observed in either mutant line. In turn, differences in CKX activity in the roots between the ckx1 and ckx3 mutants were reflected via root morphology. The decreased CKX activity in the ckx1 lines corresponded to greater root length, increased surface area, and greater numbers of root hairs, while the increased CKX activity in the ckx3 mutants gave the opposite results. RNA-seq analysis of the spike and root transcriptomes revealed an altered regulation of genes controlling cytokinin metabolism and signaling, as well as other genes that are important during seed development, such as those that encode nutrient transporters. The observed changes suggest that the knockout of a single CKX gene in barley may be not sufficient for disrupting cytokinin homeostasis or increasing grain yields.

A simple and efficient CRISPR/Cas9 platform for induction of single and multiple, heritable mutations in barley (Hordeum vulgare L.)

BACKGROUND

Genome editing of monocot plants can be accomplished by using the components of the CRISPR/Cas9 (clustered regularly interspaced short palindromic repeat/CRISPR associated Cas9) technology specifically optimized for these types of plants. Here, we present the development of RNA-guided Cas9 system for simplex and multiplex genome editing in barley.

RESULTS

We developed a set of customizable RNA-guided Cas9 binary vectors and sgRNA modules for simplex and multiplex editing in barley. To facilitate the design of RNA-guided Cas9 constructs, the pBract derived binary vectors were adapted to Gateway cloning and only one restriction enzyme was required for construction of the sgRNA. We designed a synthetic, codon optimized Cas9 gene containing the N terminal SV40 nuclear localization signal and the UBQ10 Arabidopsis 1st intron. Two different sgRNAs were constructed for simplex editing and one polycistronic tRNA-gRNA construct (PTG) for multiplex editing using an endogenous tRNA processing system. The RNA-guided Cas9 constructs were validated in transgenic barley plants produced by Agrobacterium-mediated transformation. The highest mutation rate was observed in simplex editing of the cytokinin oxidase/dehydrogenase HvCKX1 gene, where mutations at the hvckx1 locus were detected in 88% of the screened T0 plants. We also proved the efficacy of the PTG construct in the multiplex editing of two CKX genes by obtaining 9 plants (21% of all edited plants) with mutations induced in both HvCKX1 and HvCKX3. Analysis of the T1 lines revealed that mutations in the HvCKX1 gene were transmitted to the next generation of plants. Among 220 screened T1 plants we identified 85 heterozygous and 28 homozygous mutants, most of them bearing frameshift mutations in the HvCKX1 gene. We also observed independent segregation of mutations and the Cas9-sgRNA T-DNA insert in several T1 plants. Moreover, the knockout mutations of the Nud gene generated phenotype mutants with naked grains, and the phenotypic changes were identifiable in T0 plants.

CONCLUSIONS

We demonstrated the effectiveness of an optimized RNA-guided Cas9 system that can be used for generating homozygous knockout mutants in the progeny of transgenic barely plants. This is also the first report of successful multiplex editing in barley using a tRNA processing system.

Artificial MicroRNA-Based Specific Gene Silencing of Grain Hardness Genes in Polyploid Cereals Appeared to Be Not Stable Over Transgenic Plant Generations

Gene silencing by RNA interference is a particularly important tool in the study of gene function in polyploid cereal species for which the collections of natural or induced mutants are very limited. Previously we have been testing small interfering RNA-based approach of gene silencing in wheat and triticale. In this research, artificial microRNAs (amiRs) were studied in the same species and the same target genes to compare effectiveness of both gene silencing pathways. amiR cassettes were designed to silence Puroindoline a (Pina) and Puroindoline b (Pinb) hardness genes in wheat and their orthologues Secaloindoline a (Sina) and Secaloindoline b (Sinb) genes in triticale. Each of the two cassettes contained 21 nt microRNA (miR) precursor derived from conserved regions of Pina/Sina or Pinb/Sinb genes, respectively. Transgenic plants were obtained with high efficiency in two cultivars of wheat and one cultivar of triticale after using the Pinb-derived amiR vector for silencing of Pinb or Sinb, respectively. Lack of transgenic plants in wheat or very low transformation efficiency in triticale was observed using the Pina-derived amiR cassette, despite large numbers of embryos attempted. Silencing of Pinb in wheat and Sinb in triticale was highly efficient in the T1 generation. The transcript level of Pinb in wheat was reduced up to 92% and Sinb in triticale was reduced up to 98%. Moreover, intended silencing of Pinb/Sinb with Pinb-derived amiR cassette was highly correlated with simultaneous silencing of Pina/Sina in the same transgenic plants. High downregulation of Pinb/Pina genes in T1 plants of wheat and Sinb/Sina genes in T1 plants of triticale was associated with strong expression of Pinb-derived amiR. Silencing of the target genes correlated with increased grain hardness in both species. Total protein content in the grains of transgenic wheat was significantly lower. Although, the Pinb-derived amiR cassette was stably inherited in the T2 generation of wheat and triticale the silencing effect including strongly decreased expression of silenced genes as well as strong expression of Pinb-derived amiR was not transmitted. Advantages and disadvantages of posttranscriptional silencing of target genes by means of amiR and siRNA-based approaches in polyploid cereals are discussed.

[Use of naloxone in acute poisoning with opiates in substance dependent persons]

Acute poisonings with drugs of abuse in Poland in 1995 made up 3-4% of all cases of intoxications. In Kraków the most common cause of drug addiction resulting in life threatening states is the use and abuse of opiates derivatives produced by drug addicted people themselves. This domestic product, so called "kompot" or Polish heroin is produced from poppy straw or juice of poppy head (Papaver somniferum). "Kompot" shows the variable contents of heroin, 6-MAM, 3-MAM, morphine, acetylocodeine and codeine. Papaverine, thebaine and narcotine were also detected. The aim of the study was to investigate the frequency of application and the efficiency of naloxone in the treatment of acute poisonings with "kompot" in the subculture of Kraków drug abusers. 91 patients were treated in the Department of Toxicology in 1996 from the acute poisoning with "kompot". There were 24% of women and 76% of men. The age average was 25.2 years. In 61.5% of cases patients intake only "kompot", in 27.5% "kompot", benzodiazepines and barbiturates, in 6.6% "kompot" and amphetamine and only in 4.4% "kompot" with ethanol. In 10% of poisoned naloxone was applied only at the place of accident. In 58% only in the Department of Toxicology. 32% were treated with naloxone both at the place of accident and in the Department of Toxicology. At the place of accident in most cases the single dose was usually applied (mean dose 0.48 mg) and 76% of patients required the additional treatment with naloxone after the admission (mean dose 1.92 mg). Only 5.5% of acute intoxicated with kompot" drug abusers needed intensive care treatment. Complications in the form of vomiting and excitement were a rare case-5.5%.

[Dependence producing substances in the practice of the Insitute of Forensic Experts in Krakow]

Different pieces of evidence connected with drug addiction have been used as material for studies carried out at the institute of Forensic Research in Kraków since the end of the sixties. The number of expert's opinions concerning these questions is constantly on the increase. Work done by the institute in this field has led to the creation of a list of dependence producing substances and their substitutes used by addicts, the methods of illicit production, and the ways and usable forms in which they are introduced into the system. The author describes the most popular drugs and their substitutes used in Poland. The number of these substitutes is big. Among them are: different medicines (e.g. Parkopan, Aviomarin) and solvents (toluene), various vegetable raw materials (e.g. Folium Stramonli, Pallocybe semilanceata). At the same time the use of genuine narcotics like morphine derivatives originating from Papaver somniferum and Cannabis sativa products, obtained by unusual methods of domestic production, was observed. The number of cases involving amphetamine and its analogues increased last year. The presence of opium alkaloids (morphine, codeine, papaverine, thebaine and narcotine as well as acetyl derivatives of morphine (heroine, 3-monoacetylmorphine, 6-monoacetylmorphine) and codeine (acetylcodeine) was detected in "kompot" by means of TLC, HPLC and GC/MS methods. The author also presents, from the analyst's point of view, analytical and interpretational problems of drugs of abuse, and regulations connected with drug addiction and with road traffic offences.

Drug addiction in Poland and criminalistic traces

The authors describe the most popular drugs and their substitutes being used in Poland. The paper also presents the problem of developing and examining criminalistic traces in biological and some non-organic materials.