b'Apomixis could also eliminate the challenge of viruses beinging, that will allow you to cycle faster and to come up much passed through cuttings within crops that are generally propa- earlier with new products and to maybe go for more localized gated vegetatively, like potatoes.products - products that are suited for certain geographies, for Not nearly so positively, apomixis could also prove highlyexample. disruptive to the seed sector and, consequently plant breedingBiological apomixis depends on two notable genes. The investment.diplospory (DIP) gene, discovered by KeyGene in 2016, stops The thing is, if you buy an F1 [apomictic] hybrid on thethe egg cell from halving its chromosomes (a necessary step in market, you can keep on harvesting seeds from it. You cansexual reproduction). The parthenogenesis (PAR) gene, which grow that indefinitely because you dont need the parental linesKeygene announced the discovery of in dandelion just last anymore. So it really takes away that protection in the currentyear, allows an egg cell to start dividing without fertilization. system, Op den Camp says. Interestingly, though only a small number of plants use apomixis, Researchers are pursuing two avenues to achieve apomixis. Themost species have genes similar to the DIP and PAR genes, first, which has proven easier to achieve, is synthetic apomixis. which suggests creating apomixis within non-apomictic plants In simple terms, synthetic apomixis is achieved in a step-by- isnt far outside of reach.step fashion via gene editing. Op den Camps team is currently using the two gene discov-If we change the plant reproduction in this way, then we willeries in crop models. The next step, he says, is moving the find-have the first step of apomixis, Op den Camp explains. Thenings toward actual crops. Meanwhile, researchers also need to if we make this plant produce embryos spontaneously, then wecontinue analyzing the exact modes of actionthe complex and have the second step. [In rice], it is a combination of three genesinter-related systems - that allow apomixis to proceed in a crop.that have to be knocked out, or gene edited, and one geneIn the initial stages, itll be a transgenic proof of concept, and that needs to be ectopically expressed through a transgene tothen well also see routes towards non-transgenic applications. achieve apomixis.These non-transgenic applications come from a deeper under-In 2019, an international team reported that it had geneticallystanding of the biology, because if you know how things have engineered a line of rice plants that could reproduce clonally, theevolved in natural apomicts, you can take that further, he says.first synthetic apomixis in a crop. This was a major step forwardIn addition to the DIP and PAR genes, biological apomixis but, because different genes control apomixis in different typesalso depends on an additional critical component. Every seed of plants, the finding couldnt be replicated in non-grass species.is made of three parts: a seed coat (the maternal tissue), an The other limitation in synthetic apomixis is thatat leastembryo (which is sexually fertilized in most plants but includes as the technology stands right nowany clones produced areexclusively maternal genetics in apomicts), and an endosperm. the end point of breeding: they cannot be further outcrossedForming a functional endosperm seems to be, says Gehring, the because their apomictic genes will produce offspring with tootrickiest part. many chromosomes in subsequent generations. This means thatApomixis is a relatively new component of Gehrings research synthetic apomixis has the potential to speed propagation ofprogram. She and her team have studied sexual seed develop-preferred lines but cannot be leveraged further within a largerment, especially epigenetic regulation of endosperm expression. breeding program. In just the last two years, the team has begun work on apomixis. The second way to achieve apomixis is via reverse engineer- Their goal is to crack the endosperm puzzle, and Gehring says ing the underlying mechanisms that allow natural apomixis. Optheyre making progress.den Camp explains that his teams goal is to introduce biologicalThe endosperm in sexual seeds is formed through a second apomixis to non-apomictic plants, which would allow continuedfertilization event and carries an unusual ploidy: it is triploid with breeding beyond the first apomictic generation.two maternal and one paternal genomes. Natural apomicts can Some people consider fixing heterosis to be the endpoint ofform their endosperm in two ways: in some cases, via pollination breeding. But, if you use biological apomixis, its just the start, heand in other cases without.says. For a breeding scheme to make rapid progress in actualIn natural apomictsin some casesthe endosperm is breeding, meaning you have a genetic gain in every cycle youstill sexual, so its still pollinated, though the paternal side doesnt grow, having a chance to make crosses is very important, andcontribute genes to the next generation, Gehring says. In other thats only possible through biological apomixis.cases, the endosperm is formed without any fertilization.His team is currently studying the common dandelion, whichGehrings research teams goal is to achieve a functional is a known apomict with all seeds identical to the mother.endosperm that requires no paternal genome at all: an apomictic If you make a hybrid of thatwhich you can because theformed from exclusively maternal genes both within the embryo pollen is still sexual - that allows you to continue to make crossesand the endosperm. To get there, the team is employing both and continue to improve using apomixis, he explains. So oncesynthetic and biological strategies. you find something that is interesting, you can keep it as a cloneOp den Camp says he is hopefuleven confidentthat the and propagate it but if you want to continue with that material,big steps made to date will translate to a functional technology in you can just make a cross and generate new variation. In breed- the near term.DECEMBER 2023SEEDWORLD.COM /85'