Secret "weeping" exhibited by apple trees could boost fruit production with genetic engineering 

In a remarkable breakthrough that could revolutionize apple orchards, a team of plant geneticists has discovered a unique mutation in apple trees. 

This mutation, residing in a gene known as MdLAZY1A, causes the trees to exhibit a “weeping” architecture, where branches grow in a downward trajectory. 

The discovery could pave the way for boosting fruit productivity, transforming apple farming methods, and saving labor costs.

Apple farming

For over a hundred years, apple farming has incorporated a practice where growers bend the branches of young apple trees downwards to enhance crop productivity. 

While the exact scientific underpinning behind the improved yield due to branch bending is still under investigation, researchers have noted that this method redirects more resources such as carbon and other nutrients from vegetative growth – branches and leaves – towards reproductive growth which includes flowering and fruiting.

Focus of the study

Interestingly, nature exhibits some instances where trees naturally adopt this weeping growth, but these cases are rather infrequent. In the current study, published in the journal Plant Physiology, researchers set out to investigate the genetic basis behind such unusual growth patterns

Study senior author Kenong Xu is an associate professor at the School of Integrative Plant Science Horticulture Section at Cornell AgriTech in the College of Agriculture and Life Sciences.

“The findings presented in this paper could be used to make existing apple cultivars grow somewhat downwards and/or with more spreading branches, so they can be more productive, and it can save on labor costs of tying branches down,” said Professor Xu.

How the research was conducted 

The journey to identify this gene was based on a “forward genetics” approach. In this method, researchers examined observable traits in more than 1,000 offspring of weeping cultivars. 

The experts segregated these offspring based on the growth patterns exhibited, isolating weeping and normal growth. Then, leveraging advanced genetic sequencing techniques, they compared the two groups to pinpoint the genetic determinant.

Rare gene mutation 

The mutation in the gene MdLAZY1A identified in this study is not commonplace. The researchers found that less than one percent of trees have this allele or variation that incites weeping growth.

But the scarcity of this natural mutation is not a dead end for scientists. Having pinpointed this single nucleotide substitution to the MdLAZY1A gene, plant geneticists may employ the revolutionary CRISPR/Cas-9 gene-editing technology to cultivate apple tree varieties exhibiting the weeping-like growth.

“Our team confirmed this through multiple transgenic studies. We introduced that allele into a standard royal gala apple cultivar and observed the tree growing in a downward manner,” explained Xu.

More about apple trees

Apple trees (Malus domestica) are one of the most widely cultivated fruit trees in the world, prized for their crunchy, sweet fruit that has been enjoyed by humans for thousands of years. There are more than 7,500 known varieties of apples, ranging in taste from sweet to tart, and in color from deep crimson to golden yellow.

An apple tree can reach up to 12 meters in height, and they are primarily grown in cooler climates where they go dormant during the winter. Apple trees are deciduous, meaning they lose their leaves annually, and produce beautiful white to pink blossoms in the spring, which eventually give way to the fruit.

Apple trees are cross-pollinators, meaning they need other apple trees nearby to facilitate pollination. This is usually done by bees, which transport pollen from the flowers of one apple tree to another, leading to fertilization and the production of apples.

In addition to their fruit, apple trees have been historically valued for their hard, dense wood, which can be used for a variety of purposes including the crafting of furniture and musical instruments.

From a scientific perspective, apple trees have long been a subject of research, as they possess a complex genome structure. This, along with their long cultivation history, has led to a wide genetic diversity among apple varieties, each with their unique flavors, colors, and resistance to diseases.

Recent research, such as the Cornell study mentioned, aims to better understand the genetic makeup of apple trees and how certain traits, like the “weeping” growth of branches, can be manipulated to improve yield and efficiency in apple orchards. 

Such findings have significant implications for the global apple industry, potentially leading to increased productivity and decreased labor costs.

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