Apomixis (asexual seed formation)

Apomixis is a naturally occurring form of asexual reproduction through seeds in plants which presents a key technology for crop variety improvement, as it would enable the permanent fixation of any heterozygous genotype, regardless of its genomic heredity and phenotypic complexity, in a single generation.  Apomixis is rare in crop plants, and the impact on breeding programs would be enormous, as the fixation of traits demonstrating heterosis in a single generation would permit the rapid development of superior crop varieties adapted to changing environmental conditions, diverse farming niches and systems, and evolving markets.  Furthermore, present resource investment into the generation and maintenance of inbred lines could instead be redirected to the development of a more diverse germplasm. The estimated market improvement value of having apomixis introduced to rice alone would be $2.5 billion per year, not to mention true seed propagation of tuber crops (potato and cassava) through apomixis would have an estimated value of $3.2 billion per year (not corrected for 2020 market values[1]).  The multiple uses of apomixis in agriculture have long been recognized as important steps for sustainability and food security[2], although as of yet apomixis has not yet been successfully introduced into crops. 

In naturally occurring apomict plants three essential developmental events (i.e. functional elements) are genetically controlled and differ from sexual seed formation: (i) the formation of a chromosomally-unreduced egg cell via apomeiosis, (ii) parthenogenetic (i.e. without fertilization) embryonic development of this egg cell and, (iii) fertilization of the polar nuclei with male gametes to produce chromosomally balanced endosperm (i.e. pseudogamy).  The combination of these functional elements produces apomictic seeds with embryos that are genetic clones of the mother plant.

[1] Spillane, M. D. Curtis, and U. Grossniklaus, “Apomixis technology development - Virgin births in farmers’ fields?,” Nature Biotechnology. 2004, doi: 10.1038/nbt976.

[2] R. A. Jefferson and R. Bicknell, “The Potential Impacts of Apomixis: A Molecular Genetics Approach,” in The Impact of Plant Molecular Genetics, 1996.

 

My lab initiated a tangential research program in medicinal agriculture in 2005 in our former institute (IPK Gatersleben, Germany), as our apomixis work logically led us to projects on the genetic and reproductive variability of St. John’s Wort (Hypericum perforatum, an apomictic plant) and German Chamomile (Matricaria chamomilla, development of triploid breeding with industry) for the treatment of dementia and digestive problems respectively.  This work has led to significant government and industry funding to my lab over the years, in addition to many important high-impact publications and training of HQP.  As such, my lab is expanding into a larger Medicinal Agriculture program which connects with many faculties at USask (e.g. Cannabinoid Research Initiative of Saskatchewan) to generates funding and job creation for Saskatchewan.  In this light we have recently received funding for both Cannabis and Wild Rice breeding, the latter of which has an almost exclusive Indigenous industry component.  A strong aspect of this developing program will be the use and respect of traditional plants and Indigenous knowledge.

The United Nations has projected that by 2050 the global population will surpass 9.7 billion individuals, an 25% increase from today’s 7.8 billion.  This rise in population will increase the strain on multiple industries involved in many aspects of food production, particularly in crops used for human and animal consumption. Moreover, the compounded growth in human population, agricultural lands and water scarcity require significant improvements in sustainable agronomic practices, the development of high yielding resilient varieties and importantly, in diversifying crops in human and animal diets.

Triticale (X Triticosecale Wittmack) is a man-made interspecific hybrid of wheat (Triticum durum, T. aestivum) and rye (Secalecereale) which has many advantages over other cereal crops, for example a high level of resistance to biotic stresses (rusts, powdery mildew and leaf spot) and abiotic stresses such as drought, lodging and winter hardiness. In addition, it expresses high grain and forage yield potential under diverse growing conditions, suggesting it could be a viable option for enhancing global cereal production.

This project is based upon the unique opportunity present by a large and valuable collection (The E.N. Larter collection) of primary triticale (wheat x rye crosses) accessions and their parental lines which were generated at University of Manitoba from 1954 to the 1990’s.  This collection is maintained in the Plant Gene Resources of Canada (PGRC) at AAFC Saskatoon, and is the core of the germplasm in this work.  While the entire Larter collection has more than 1300 records, we will focus on the material planted (940 lines) in the field in 2019 and 2020, of which only 757 are classified as “Triticum cross” (i.e. Triticale).  Furthermore, at least 50 of these supposed triticales appear to be wheat species (Diederichsen, pers. obs.).  The key findings coming from this study will enable us to select promising lines for triticale breeding improvement.

The enormous diversity of seed traits is an intriguing feature that contributes to the success of higher plants, not to mention potentially useful traits for crop breeding. For example, seed mass (thousand kernel weight) is considered key for seedling development and reflects maternal provisioning of developing embryos via the endosperm, as seed mass likely has an optimum for resource allocation. Importantly, this means that the triticale collection here represent “natural mutational laboratories” for identifying factors controlling endosperm development, which could subsequently be applied to other crop plants.