Decreased vegetative branching in cultivated tomato
Greenhouse tomato cultivation is an important contributor to the Dutch economy and in order to remain so, innovations leading to a decrease in input with equal or increased yield are of great importance. This project aims at reducing labour input in greenhouse tomato cultivation by developing tomato plants that require less or no removal of axillary shoots (Dutch: “dieven”). An additional advantage of having tomato plants without axillary shoots is that infection by pathogens at the wound sites caused by their removal can be avoided. The objective of the project is to develop such plants by increasing the expression of tomato genes that suppress, although not sufficiently (and hence the required labour), the outgrowth of these axillary shoots. A number of such shoot outgrowth-suppressing genes is known from the model plant Arabidopsis and/or from tomato, and these will be targeted in tomato in this project. The innovative method to be used to achieve this higher expression is the exploring of the use of CRISPR/Cas9-mutagenesis for the generation of a large variety of deletions in the genes’ regulatory sequences, particularly their promoters. By removing promoter elements that are involved in suppression of gene expression, the expression level of the genes may be increased. As alternative approach, up- and downstream acting transcription factors will be identified and mutagenized.
The project contributes to the missions, in particular: “ST2 Biotechnologie en Veredeling”
• A new strategy to fine-tune expression of genes underlying important crop traits
• Enhanced insight into the regulation of lateral shoot outgrowth in cultivated tomato
• Tomato plants with no or substantially reduced lateral shoot outgrowth, contributing to less labour input and preventing crop injury
Greenhouse-cultivation tomato involves so-called indeterminate cultivars growing as a single long vine continuously renewing the main stem by sympodial growth. Outgrowth of lateral or axillary shoots (suckers; Dutch: “dieven”) in vegetative parts of the plant other than the sympodial shoot, referred to as ‘branching’, is undesirable since these shoots withdraw assimilates from primary fruit production and require manual removal. This manual removal comprises 7-10% of all the labour (costs) from planting to harvesting in Dutch tomato production and is estimated to account for 1000-1200 fte for the Dutch greenhouses (source: Plantum). Furthermore, removing the axillary shoots leads to a wound that can act as an entry point for pathogens. Thus, prevention of outgrowth of the axillary shoots would contribute to a more sustainable tomato production with lower production costs and less labour, which is becoming scarce, and with a more resilient crop as final product.
The generated mutant plants may be used either directly as starting material in breeding programs, or the regulatory regions and transcription factors identified here could be targets for more conventional mutagenesis methods. Thus, the intended results of the project, tomato plants that require less labour input, will contribute to the sustainability of tomato cultivation. Additionally, if the novel approach proves to be successful, this concept and approach may be applied in a wide range of genes, traits, and crop species in the future.