Are Giant Tomatoes the Future of Climate-Resilient Crops?

Gigantism, a common domestication trait in many crops, triggers a disproportionate growth in edible parts like stems, leaves or fruits. In a recent study by Mateus Vicente and colleagues, published in Annals of Botany, the researchers at the University of São Paulo in Brazil identified the locus that controls vegetative and reproductive organ size in tomato. 

Tomato, scientifically known as Solanum lycopersicum, has distinguished itself as a model of fruit gigantism. Although numerous genes have been identified as responsible for this particular trait in tomatoes, the genetic basis of gigantism beyond fruits to other vegetative organs, known as isometric gigantism, have remained relatively unexplored. 

Brazilian researchers identified a critical 0.4 million base pair region on chromosome 7 using introgression lines (ILs) sourced from the wild Solanum pennellii in two distinct tomato genetic backgrounds: the well-known cv. M82 and the diminutive cv. Micro-Tom. This region, named ORGAN SIZE (ORG), was meticulously fine-mapped using cutting-edge genotype-by-sequencing techniques. 

Interestingly, the research team found that ORG overlaps with previously identified Quantitative Trait Loci (QTL) controlling tomato fruit weight during domestication and breeding. This suggests that selection for larger fruits during domestication may have accidentally influenced vegetative organ size as well. 

The findings suggest that alleles derived from the wild species led to a reduction in cell number across various organs, and that this reduction was compensated to some extent by a significant increase in cell expansion within leaves, but not in fruits. Consequently, this fact led to a proportional decrease in size for leaves, flowers, and fruits in ILs carrying the alleles inherited from the wild species.  

We showed that the common denominator for the reduced size of vegetative and reproductive organs in ORG is a reduction in the number of cells, possibly through alteration of cell division rate, as suggested by histological characterizations and gene expression analyses for CYCB2;1, FW2.2 and FW3.2.

Vicente et al. 2023

As the world struggles with the effects of climate change and the need to improve food security, the identification of locus like ORG brings up interesting opportunities for adjusting the size of vegetative organs in tomato plants. By further elucidating the genetic mechanisms behind gigantism, scientists will be able to improve agricultural practices, developing crops better suited to thrive in diverse environmental conditions. 

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Vicente M.H., MacLeod, K., Zhu, F., Rafael, D., Figueira, A., Fernie, A., Mohareb, F., Kevei, Z., Thompson,A., Zsögön, A., and Pereira Peres L. (2023) “The ORGAN SIZE (ORG) locus modulates both vegetative and reproductive gigantism in domesticated tomato” Annals of Botany.  Available at: https://doi.org/10.1093/aob/mcad150