Fine-tuning 'dosage' of mutant genes unleashes long-trapped yield potential in tomato plants

Using gene editing in addition to cross-breeding to fine-tune in addition to improve yield in domesticated tomato plants, a team at CSHL was able to grow a hybrid variety which branched weakly – here providing two stems coming from which fruits can be set – to provide about twice as many fruits. Credit: Cold Spring Harbor Laboratory

Breeding in plants in addition to animals typically involves straightforward addition. As beneficial brand new traits are discovered—like resistance to drought or larger fruits—they are added to existing prized varieties, delivered via cross-breeding. nevertheless every once in a while, adding a beneficial brand new trait can result in a net subtraction, due to processes deeply hidden within the interactions of genes underlying existing in addition to newly added traits.

Interactions among genes – both positive in addition to negative—will be called epistasis (“ep-i-STAY-sis”). Today, a team of plant geneticists at Cold Spring Harbor Laboratory (CSHL) publishes a paper in Cell demonstrating how bringing together beneficial traits can have negative consequences. They discover in addition to dissect a case of negative epistasis in a variety of the tomato plant. nevertheless they also show how to exploit which knowledge to derive untapped yield potential coming from the plant. They do so by cross-breeding specimens of the plant carrying different “dosages” of gene variants responsible for positive in addition to negative traits.

“Our study provides the first example of which we’re aware of a domestication gene which hindered crop improvement,” says CSHL Associate Professor Zachary Lippman, who led the research. “which work illustrates how gene dosage can be exploited to fine-tune in addition to improve major yield traits. which shows which by identifying in addition to dissecting similar cases of negative epistasis in plant in addition to animal breeding, we may be able to break existing productivity barriers in agriculture.”

A tale of two mutations

Nearly all tomatoes grown today – possibly every one you’ve ever eaten – carries a gene mutation which likely arose 8,000 to 10,000 years ago, at the dawn of agriculture. which ancient mutation caused early forms of domesticated tomato plants to produce fruits with larger green leafy caps on top. We’ll never know for sure why ancient tomato growers liked their tomatoes with larger caps, nevertheless we do know which they selected for such plants, in addition to crossed them in order which the trait became part of the genome in most modern tomato varieties.

The second mutation tracked down by Lippman’s team which interacts with which ancient mutation was discovered from the mid-twentieth century, first spotted in domesticated tomatoes planted in a field owned by the Campbell Soup Company. which second mutation caused two dramatic alterations. Called jointless, the newly mutated gene changed the elbow-like bend from the stem leading to the plant’s flowers – a natural joint called an abcission zone. These mutant tomato plants, as “jointless” implies, had no joints.

Left: A typical wild tomato plant. Note the simple branches (inflorescences) which lead to several flowers each; in addition to the jointed stem (green asterisk in inset) where the fruit will be attached to the branch. Right: mutations in genes which regulate plant architecture result in many more flowers, due to the many branching events marked by red arrowheads. Note from the inset which the stem attaching the fruit to the plant will be “jointless.” To breeders, the former trait will be highly undesirable; the latter will be desirable. By tweaking gene dosages, Lippman’s CSHL team has figured out a way to keep “jointless” while inducing weak branching – a “sweet spot” capturing untapped yield. Credit: Cold Spring Harbor Laboratory

which was a wonderful trait for industrial growers, who by the postwar period wanted to harvest fruit with mechanical pickers. which’s much easier for a harvester (mechanical or human) to cleanly detach the tomato coming from the vine from the jointless variety, since the elbow from the stem vanishes in addition to the green cap on top of the fruit remains on the plant. When tomatoes are tossed into a container as they are picked, those with caps in addition to bits of residual stem often puncture additional tomatoes nearby. So growers liked jointless in addition to breeders sought to exploit which immediately.

nevertheless the ancient mutation which enlarged the green caps prevented the easy adoption of jointless. For reasons unknown to breeders in addition to growers, in addition to not known until the newly published research coming from CSHL, jointless plants frequently had too many of the branches which make flowers, known as inflorescences.

“You could think – correctly – which more inflorescence branches mean more flowers,” says Lippman, “in addition to in fact which’s one way to get more yield. nevertheless only up to a point. If tomato or any additional plant makes too many flowers, the plant doesn’t have enough resources to turn all those flowers into fruits. The result will be actually a decline in fertility.”

Commercial breeders eventually found a way to counteract the unwanted branching, which enabled them to take advantage of the mutation which generated jointless stems. The result was inflorescences shaped in a way familiar to anyone who has ever seen tomatoes on the vine. The fruits hang off single stems, arrayed in a linear zig-zag pattern.

Reversing a negative gene interaction

“Our team wanted to better understand the genetic underpinnings of the relation between inflorescence branching in addition to yield,” Lippman explains. They reasoned which by understanding the interaction of genes responsible for branching in addition to flowering, “we might, from the case of jointless, come up having a type which’s a little bit more balanced – one which could branch a little bit. Weak branching could mean a few more flowers in addition to fruits, while not overtaxing the plant. Yield could increase.”

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CSHL Associate Professor Zach Lippman describes how his team demonstrated which bringing together beneficial traits can sometimes have negative consequences. He explains how understanding which phenomenon can overcome ancient barriers in agriculture. Credit: Cold Spring Harbor Laboratory (CSHL)

which will be exactly what he in addition to colleagues succeeded in doing. Their key discovery: realizing which the ancient mutation which makes larger green caps in most modern tomato plants interacts with the jointless mutation first noticed from the Campbell Soup field some decades ago. which interaction will be a telling example of “negative epistasis,” says Lippman – “a case of two mutations, one ancient in addition to one recent, both considered beneficial when they were selected, when placed from the same plant have a negative effect.”

By totally negating the trait conferred by jointless which was unwanted – which explosion of branching —”we think breeders missed some important potential in yield.” The team was able to capture in addition to exploit which potential by adjusting the “dosage” of the gene responsible for the size of the green cap. Rather than zeroing-out its impact on branching, like commercial growers did, they were able to make genetic crosses with variants carrying different versions (called alleles) of the gene, in order which only a fraction of its power to spur branching will be expressed.

The result will be a weakly branching tomato variety which will be also jointless, hence easy to harvest. Yet they also have more fruits, simply because they develop just a few more branches in addition to flowers.

which strategy of identifying, neutralizing in addition to potentially exploiting negative epistasis, says Lippman, could help improve additional crops, in addition to also perhaps domesticated animals in which there may be more hidden gene interactions with less obvious negative effects which are preventing breeders in addition to farmers coming from realizing their full genetic potential.

“Bypassing negative epistasis on yield in tomato imposed by a domestication gene” appears online in Cell May 18, 2017. The authors are: Sebastian Soyk, Zachary H. Lemmon, Matan Oved, Josef Fisher, Katie L. Liberatore, Soon Ju Park, Anna Goren, Ke Jiang, Alexis Ramos, Esther van der Knaap, Joyce Van Eck, Dani Zamir, Yuval Eshed, in addition to Zachary B. Lippman.

Explore further:
Gene editing yields tomatoes which flower in addition to ripen weeks earlier

More information:
“Bypassing negative epistasis on yield in tomato imposed by a domestication gene” Cell, May 18, 2017. , DOI: 10.1016/j.cell.2017.04.032

Journal reference:

Provided by:
Cold Spring Harbor Laboratory

Fine-tuning 'dosage' of mutant genes unleashes long-trapped yield potential in tomato plants

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