Researchers identified a protein that helps tomato plants respond to shade, regulate photosynthesis and maintain fruit production under high-density growing conditions.
Researchers have identified a gene that could help breeders develop tomato varieties that use light more efficiently and produce higher yields.
Scientists from Argentina’s National Scientific and Technical Research Council (CONICET) found that tomato plants use the SlBBX20 protein as a biological switch to detect shade from neighbouring plants and adjust their growth.
The discovery, published in Plant Physiology and Biochemistry, could be particularly relevant in high-density tomato production, where plants compete for the sunlight needed for photosynthesis.
“The results of this work show that this protein is essential for the plant to optimize the light harvest to make photosynthesis and adjust its yield in response to the shade,” says Javier Botto, leader of the study and a CONICET researcher at the Institute of Physiological and Ecological Research Linked to Agriculture (IFEVA, CONICET-UBA).
Potential Target for Tomato Breeding
The researchers found that SlBBX20 influences plant height, hormone activity, photosynthesis and ultimately tomato yield. This makes the gene a potential target for breeding more efficient, productive commercial varieties, according to a press release.
“This study allowed us to identify a gene that regulates growth by affecting its hormones and photosynthesis, and consequently alters the yield of tomato plants. These results open up the possibility of using this gene as a molecular target to develop more efficient and high-yielding commercial varieties of tomatoes (and other crops),” says Botto, who leads the Plant Development Plasticity laboratory at IFEVA and has a doctor in Biological Sciences.
Protein Helps Plants Respond to Shade
The SlBBX20 gene contains the instructions for producing the protein of the same name. Researchers found that tomato plants lacking the protein were largely unable to increase their height when shaded by neighbouring plants.
“Our work showed that those plants that lack this protein almost completely lose their ability to grow in response to the shade,” says Mariano Mejía, first author of the study, agricultural engineer and CONICET doctoral scholarship holder.
The loss of the protein also affected the plants’ stomata—the pores through which carbon dioxide enters and water vapour exits. Plants without SlBBX20 developed fewer stomata and opened them less frequently, reducing photosynthesis and fruit production.
“In addition, by not being able to properly regulate their biological processes in response to light, plants without this protein do less photosynthesis, because they have and open their stomatic pores less, where carbon dioxide (CO2) enters the plant and water vapor leaves the environment and, as a direct consequence, they produce less fruit,” Mejía says.
Supporting Photosynthesis in Bright Conditions
Researchers also found that SlBBX20 promotes the expression of genes involved in producing anthocyanins, the pigments responsible for violet and bluish colours in plant leaves, stems and fruits. These pigments help protect plants against damage caused by intense light.
The SlBBX20 protein “improves the expression of the biosynthesis genes of pigments known as anthocyanins that give violet/bluish tones to leaves, stems and fruits. These natural pigments act as ‘sunscreen’ and antioxidants for the plant, reducing the inhibitory effects due to high light intensity on photosynthesis,” says Gabriel Gomez Ocampo, also first author of the study, doctor in Agricultural Sciences and CONICET postdoctoral fellow.
“This is beneficial because it allows the plant to harvest more light and synthesize more essential carbohydrates for its growth that results in greater production of tomatoes in open and bright environments,” he says.
Edited Plants Produced Fewer Tomatoes
To determine the function of SlBBX20, the researchers compared wild tomato plants with edited plants in which expression of the gene had been blocked.
Both groups were grown under several light conditions. Researchers simulated shade using specialized lights and filters and created natural shading by increasing plant density in growth chambers and a greenhouse.
“When studying the edited plants that were blocked from the expression of the SlBBX20 gene, we observed that they completely lost the ability to grow in response to the shade. These plants developed fewer stomal pores and suffered a drastic drop in their levels of auxins, key growth hormones, along with a lower production of photoprotective pigments, which resulted in less photosynthesis and finally in a loss in the quantity and weight of the tomatoes produced,” explains Botto.
The findings suggest SlBBX20 could provide breeders with a molecular target for improving how tomato plants capture light and allocate carbohydrates to fruit production.
“The discovery of the role of this gene would allow the development of tomato crops that maximize the use of photosynthetic carbohydrates to produce more fruits,” Botto concludes.
Researchers from IFEVA, the University of Buenos Aires Faculty of Agronomy, Palacký University’s Institute of Experimental Botany in the Czech Republic and the University of São Paulo’s Institute of Biosciences in Brazil also participated in the study.
