Smart Canopies: Revolutionizing Maize Yields with the lac1 Gene Mutation
Corn, or maize, is a staple food in several countries. Corn is a versatile food, inexpensive, and easy to store. Therefore, to combat hunger in several countries, increasing maize yields is key. Intuitively, increasing plant density, or the amount of maize that is planted, also results in higher yields. However, when planting more corn, optimizing plant architecture is key. The corn needs to be planted in such a way that the leaves of the crops that are taller do not block light to the lower plants. Generally, increasing plant density causes distinct sunlight levels for each level (high, medium, low) of maize. This difference in sunlight is problematic because the lower plants do not grow as well with less sunlight. Therefore, the solution to this obstacle is finding a way to differentiate the angles of the leaves and canopies of the maize to ensure that all levels of corn receive adequate sunlight. This group of scientists at China Agricultural University found a natural mutant that results in a “smart canopy”, angling the leaves such that all parts of the maize receive sunlight.
A natural mutant is a mutation that was generated during the evolution of a species–there is no human involvement. The “smart canopy” that these scientists found is named the leaf angle architecture of smart canopy 1 (lac1). This mutant results in “upright upper leaves, less-erect middle leaves and relatively flat lower leaves” (see figure below). After tests in the field, the mutant performed well and the plants with the mutant experienced high levels of photosynthetic efficiency and less shade avoidance when compared with the wild plants. Essentially, the plants with the mutant present experienced more light penetration across the plant.
But, where did the mutation come from? The lac1 mutation is caused by the gene DWF4. DWF4 is involved in making the hormone brassinosteroid, which is responsible for controlling the leaf angles. According to Tian and others, “The lac1 gene is dynamically regulated by shade to control the angle of the upper leaves at various planting densities.” When the gene senses more shade, it “tells”, or sends a signal, to the plant to angle the upper leaves more, resulting in more light for the lower leaves. This quality is what earns this mutation the title of “smart canopy”: the dynamic regulation aspect of the mutant–the ability to change the angle of the leaves based on the sensation of shade–makes the plant able to respond to real-time information, resulting in a “smart canopy”. Technically, the way the lac1 gene is able to sense the shade is through the light-sensitive phytochrome A (phyA) photoreceptors. These photoreceptors accumulate in the shaded leaves, interact with a transcription factor RAVL1, and the phyA-RAVL1 interaction activates lac1, decreasing brassinosteroid levels, reducing the angles of the leaves.
Clearly, the “smart canopy” created by lac1 has potential to increase maize yields by augmenting without the setbacks of poor light penetration. However, the next question is how to rapidly introduce the lac1 gene into commercial maize.Traditionally, a process called introgression is used to incorporate a new gene or variety into a species. Introgression is when alleles, or versions of the same gene, are incorporated into a species using hybridization. However, introgression is generally a time-consuming and arduous process. One approach that these scientists suggested to hasten the process is haploid-induction editing. In this method, a special corn plant called a "haploid inducer" is used to make seeds that only have the maternal chromosomes. Then, these seeds are treated so their chromosomes double back to normal. This process was made easier by adding the lac1 gene-editing tools directly into the haploid inducer. This modified haploid inducer was crossed with 43 different types of corn plants. Out of those, 20 types successfully got the mutated lac1 gene. Five of these edited lines were planted in a field and resulted in the smart canopy plant architecture.
This study performed field tests over four years with highly positive results. The implication is that this natural mutant, lac1, has high potential to effectively increase crop yields under high planting densities, and has the ability to be rapidly incorporated into current maize lines. While further testing of lac1 in commercial varieties is needed, and the efficiency of the genetic transformation and haploid-induction editing system can be further optimized, lac1 serves as a valid genetic framework for architectural engineering of smart canopies in maize. This breakthrough could play a vital role in improving global maize production and addressing food security challenges.
Sources:
https://www-nature-com.horacemann.idm.oclc.org/articles/d41586-024-03189-5