Abstract
The C4 crop maize (Zea mays) is the most widely grown cereal crop worldwide and is an essential feedstock for food and bioenergy. Improving maize yield is important to achieve food security and agricultural sustainability in the 21st century. One potential means to improve crop productivity is to enhance photosynthesis. ictB, a membrane protein that is highly conserved across cyanobacteria, has been shown to improve photosynthesis, and often biomass, when introduced into diverse C3 plant species. Here, ictB from Synechococcus sp. strain PCC 7942 was inserted into maize using Agrobacterium-mediated transformation. In three controlled-environment experiments, ictB insertion increased leaf starch and sucrose content by up to 25% relative to controls. Experimental field trials in four growing seasons, spanning the Midwestern United States (Summers 2018 & 2019) and Argentina (Winter 2018 & 2019), showed an average of 3.49% grain yield improvement, by as much as 5.4% in a given season and up to 9.4% at certain trial locations. A subset of field trial locations was used to test for modification of ear traits and ФPSII, a proxy for photosynthesis. Results suggested that yield gain in transgenics could be associated with increased ФPSII, and the production of longer, thinner ears with more kernels. ictB localized primarily to the microsome fraction of leaf bundle-sheath cells, but not to chloroplasts. Extramembrane domains of ictB interacted in vitro with proteins involved in photosynthesis and carbohydrate metabolism. To our knowledge, this is the first published evidence of ictB insertion into a species using C4 photosynthesis and the largest-scale demonstration of grain yield enhancement from ictB insertion in planta. Results show that ictB is a valuable yield gene in the economically important crop maize, and are an important proof of concept that transgenic manipulation of photosynthesis can be used to create economically viable crop improvement traits.
Highlights
Maize (Zea mays subs. mays) is the most widely grown cereal crop in the world with 194M ha planted worldwide in 2018, and the United States is the largest grower of maize accounting for 34% of the world’s production in 2018 (392M tonnes) [1]
We demonstrate that ictB insertion into maize does enhance photosynthesis, carbohydrate production and yield, with improvements observed across multiple growing environments, years, locations, and germplasm
This study investigated whether the insertion of ictB into the C4 crop maize would lead to improved photosynthesis, carbohydrate production, and yield, as previous studies have demonstrated in C3 crops
Summary
Maize (Zea mays subs. mays) is the most widely grown cereal crop in the world with 194M ha planted worldwide in 2018, and the United States is the largest grower of maize accounting for 34% of the world’s production in 2018 (392M tonnes) [1]. Transgenic improvement of photosynthesis has led recently to increased biomass production in field trials of C3 crops [7] such as tobacco (Nicotiana tabacum) [8,9] and rice (Oryza sativa) [10]. Unlike these species, maize uses C4 photosynthesis, as do two other economically important crops, sugarcane (Saccharum officinarum) and sorghum (Sorghum bicolor), and multiple candidate bioenergy grasses such as miscanthus (Miscanthus) and switchgrass (Panicum virgatum). The unique biochemistry of C4 photosynthesis provides several opportunities for improvement [11]
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