The Effect of Caffeine and Trifluralin on Chromosome Doubling in Wheat Anther Culture

Anther Culture Protocols for Barley and Wheat

Doubled haploid (DH) techniques remain valuable tools for wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) genetic improvement, and DH populations are used extensively in breeding and research endeavors. Several techniques are available for DH production in wheat and barley. Here, we describe two simple, robust anther culture methods used to produce more than 15,000 DH wheat and barley lines annually in Australia.

Paclitaxel and Caffeine-Taurine, New Colchicine Alternatives for Chromosomes Doubling in Maize Haploid Breeding

The doubled haploid (DH) technology is employed worldwide in various crop-breeding programs, especially maize. Still, restoring tassel fertility is measured as one of the major restrictive factors in producing DH lines. Colchicine, nitrous oxide, oryzalin, and amiprophosmethyl are common chromosome-doubling agents that aid in developing viable diploids (2n) from sterile haploids (n). Although colchicine is the most widely used polyploidy-inducing agent, it is highly toxic to mammals and plants. Therefore, there is a dire need to explore natural, non-toxic, or low-toxic cheaper and accessible substitutes with a higher survival and fertility rate. To the best of our knowledge, the advanced usage of human anticancer drugs "Paclitaxel (PTX)" and "Caffeine-Taurine (CAF-T)" for in vivo maize haploids doubling is being disclosed for the first time. These two antimitotic and antimicrotubular agents (PTX and CAF-T) were assessed under various treatment conditions compared to colchicine. As a result, the maximum actual doubling rates (ADR) for PTX versus colchicine in maize haploid seedlings were 42.1% (400 M, 16 h treatment) versus 31.9% (0.5 mM, 24 h treatment), respectively. In addition, the ADR in maize haploid seeds were CAF-T 20.0% (caffeine 2 g/L + taurine 12 g/L, 16 h), PTX 19.9% (100 μM, 24 h treatment), and colchicine 26.0% (2.0 mM, 8 h treatment). Moreover, the morphological and physiological by-effects in haploid plants by PTX were significantly lower than colchicine. Hence, PTX and CAF-T are better alternatives than the widely used traditional colchicine to improve chromosome-doubling in maize crop.

Functional identification of purine permeases reveals their roles in caffeine transport in tea plants (Camellia sinensis)

Caffeine is a characteristic secondary metabolite in tea plants. It confers tea beverage with unique flavor and excitation effect on human body. The pathway of caffeine biosynthesis has been generally established, but the mechanism of caffeine transport remains unclear. Here, eight members of purine permeases (PUPs) were identified in tea plants. They had diverse expression patterns in different tissues, suggesting their broad roles in caffeine metabolism. In this study, F1 strains of "Longjing43" ♂ × "Baihaozao" ♀ and different tea cultivars were used as materials to explore the correlation between caffeine content and gene expression. The heterologous expression systems of yeast and Arabidopsis were applied to explore the function of CsPUPs. Correlation analysis showed that the expressions of CsPUP1, CsPUP3.1, and CsPUP10.1 were significantly negatively correlated with caffeine content in tea leaves of eight strains and six cultivars. Furthermore, subcellular localization revealed that the three CsPUPs were not only located in plasma membrane but also widely distributed as circular organelles in cells. Functional complementation assays in yeast showed that the three CsPUPs could partly or completely rescue the defective function of fcy2 mutant in caffeine transport. Among them, transgenic yeast of CsPUP10.1 exhibited the strongest transport capacity for caffeine. Consistent phenotypes and functions were further identified in the CsPUP10.1-over-expression Arabidopsis lines. Taken together, it suggested that CsPUPs were involved in caffeine transport in tea plants. Potential roles of CsPUPs in the intracellular transport of caffeine among different subcellular organelles were proposed. This study provides a theoretical basis for further research on the PUP genes and new insights for caffeine metabolism in tea plants.

Applications of In Vitro Tissue Culture Technologies in Breeding and Genetic Improvement of Wheat

Sources of new genetic variability have been limited to existing germplasm in the past. Wheat has been studied extensively for various agronomic traits located throughout the genome. The large size of the chromosomes and the ability of its polyploid genome to tolerate the addition or loss of chromosomes facilitated rapid progress in the early study of wheat genetics using cytogenetic techniques. At the same time, its large genome size has limited the progress in genetic characterization studies focused on diploid species, with a small genome and genetic engineering procedures already developed. Today, the genetic transformation and gene editing procedures offer attractive alternatives to conventional techniques for breeding wheat because they allow one or more of the genes to be introduced or altered into an elite cultivar without affecting its genetic background. Recently, significant advances have been made in regenerating various plant tissues, providing the essential basis for regenerating transgenic plants. In addition, Agrobacterium-mediated, biolistic, and in planta particle bombardment (iPB) gene delivery procedures have been developed for wheat transformation and advanced transgenic wheat development. As a result, several useful genes are now available that have been transferred or would be helpful to be transferred to wheat in addition to the current traditional effort to improve trait values, such as resistance to abiotic and biotic factors, grain quality, and plant architecture. Furthermore, the in planta genome editing method will significantly contribute to the social implementation of genome-edited crops to innovate the breeding pipeline and leverage unique climate adaptations.

Developments and prospects for doubled haploid wheat

Doubled haploid production is a valuable biotechnology that can accelerate the breeding of new wheat varieties by several years through the one-step creation of 100% homozygous plants. The technology also plays important role in studying the genetic control of traits in wheat, in marker-assisted selection, in genomics and in genetic engineering. In this paper, recent advances in androgenesis and gynogenesis techniques, emphasizing predominantly the in vitro culture phase, as well as the emerging innovative approaches in researching and producing wheat doubled haploids are reviewed. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based genome editing, that allows targeted mutagenesis and gene targeting, is being tested extensively as a powerful and precise tool to induce doubled haploids in wheat. The review provides the reader with recent examples of gene modifications in wheat to induce haploidy.

Effect of silver nitrate and growth regulators to enhance anther culture response in wheat (Triticum aestivum L.)

Application of chemical substances as stress pre-treatment factors may positively influence androgenetic responses in cereal and other crops. AgNO₃ is an anti-ethylene compounds that played a significant role in combination with other chemicals for anther culture responses in cereal and other crop plants. For this study two local wheat cultivars viz. Kheri and Akbar were considered to evaluate the effect of AgNO₃ and to optimize the suitable doses of plant growth regulators, amino acids and sucrose that supplemented in MS medium. Data were recorded on the basis of embryoids induction, regenerated green and albino plants. The results clearly stated that anther culture responses and its major outcomes on regeneration significantly increased with suitable dosages of chemicals. The most noteworthy increases embryo like structures and regenerated green plants accomplished by utilizing the combined effect of AgNO₃ (50 mg/l) and as plant growth regulators IAA (1.0 mg/l) + kinetin (0.5 mg/l). Best embryo like structures (79.17%) and green plants (33.33%) were recorded in Kheri. The results clearly stated that reducing albinism and increasing embryos induction and green plants 50–75 mg/l silver nitrate along with optimum doses of IAA and kinetin showed very effective results in wheat.

Production of Wheat Doubled Haploids Through Intergeneric Hybridization with Maize

The intergeneric hybridization of wheat (Triticum aestivum L.) with maize (Zea mays L.) enables the production of doubled haploids (DHs) of wheat from all wheat hybrids with high efficiencies. Wheat and maize donor plants are raised in environmentally controlled greenhouses until crossing. Before anthesis, wheat spikes are emasculated and then pollinated with maize. Auxin is applied to each individual wheat floret 1 day after pollination. About 2 weeks after crossing, in vitro embryo culture is performed, enabling the regeneration of haploid wheat plantlets after maize chromosome elimination. Haploid plantlets are transferred to the greenhouse and after recovery, their genome is doubled with colchicine. Haploid plantlets can be sampled for DNA extractions and molecular analyses to aid the rapid discard of undesirable plantlets. Doubled haploid plants are raised in a greenhouse until maturity. Seeds of each fertile DH are harvested and often sown the same year. Several cycles of multiplication and evaluation in replicated plot trials and different geographical locations are then done to select the best candidate(s) for varietal registration.