In vitro-based doubled haploid production: recent improvements

Abstract

The doubled haploid system is the fastest way of hybrid variety production and plays an important role in breeding programs and developmental studies. The most commonly used methods of haploid induction, leading to haploid plants in vitro through the plant tissue/cell culture, are named as the in vitro -based (IVB) methods. These methods have been established in many of the important crops, such as barley, pepper, rapeseed, rice, sugar beet, and wheat. There are ongoing researches to optimize and improve the efficiency of these methods by focusing on factors involved in induction and regeneration phases. These factors mainly include plant genotype, the surrounding environment of parental plants, components of culture medium, the developmental stage of initial gametophytic cells, physical treatments (cold pre-treatment, heat shock) of cultured gametophytic cells, and application of different additives and plant growth regulators. Stress treatment is one of the important prerequisites for stimulation of gametophytic cells to switch towards the sporophytic pathway. However, autophagy and programmed cell death, oxidative stress, and production of reactive oxygen species (ROS) are the major limiting factors in stress-induced embryogenesis. The positive effect of different additives, such as plant growth regulators, chlormequat, polyamines (putrescine, spermidine, and spermine), stress hormones (abscisic acid, jasmonic acid, salicylic acid), DNA demethylating agents and histone deacetylase inhibitors, cellular antioxidants, cell wall remodeling agents (arabinogalactan-proteins), and compatible solutes (proline and chitosan), has been proved on the efficiency of haploid induction through IVB methods. Different mechanisms have been reported through which the aforementioned additives can enhance tolerance to embryo-inducing stresses in plants, and subsequently increase the efficiency of induction phase of IVB methods of haploid induction. Finding the best combination/interaction of inductive stresses and their corresponding chemical enhancers is crucial for successful haploid induction through IVB methods. In the present review, we highlighted recently applied additives to enhance the efficiency of the major IVB methods of haploid induction in different plants. Other potentially applicable additives, those are involved in preventing ROS accumulation, ethylene inhibitors, activating of antioxidant enzyme activity, detoxification capacity, and defense response signal pathway, which could be useful in IVB haploid induction are also discussed. The presented information could be useful to improve the efficiency of developed IVB protocols and/or to develop new protocols in recalcitrant species/genotypes.