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Development and drought responses of tomato exodermis

Periodic Reporting for period 1 - TOMATO EXODERMIS (Development and drought responses of tomato exodermis)

Reporting period: 2018-09-01 to 2020-08-31

Understanding plant development and responses to the environment is key for improving crop yields and ensuring food and fuel for the future. In the face of environmental stresses, plant development changes in order for the plant to acclimate and survive these challenges. Globally, precipitation patterns have altered drastically, and increasing numbers of crop species are being impacted by unexpected drought or flooding. For example, crop losses to drought in 2017 are estimated to cost €1 billion in Italy alone. In addition, soil salinity is on the rise, leading to root osmotic stress and plant death. All of these abiotic stresses affect root development drastically, and certain species have evolved adaptations that make them more tolerant. One of these adaptations is the exodermis, a water- and air-proofed cell layer in the root that protects it from drying and drowning.

TOMATO EXODERMIS built on recently created dataset of tomato cell type-specific gene expression and set out to address two key questions regarding the exodermis cell layer development in tomato:
1) What are the genes that are involved in exodermal development?
2) How are exodermal drought responses regulated?

By addressing these questions, it is possible to start building knowledgebase required for breeding and agricultural applications that target exodermis as a drought-protective trait. During TOMATO EXODERMIS, we were able to address the first objective (Kajala et al, https://doi.org/10.1016/j.cell.2021.04.024) but due to Covid-19 limitations (e.g. no/restricted access to the lab space), the second objective is not fully addressed but continues as an ongoing project.
During TOMATO EXODERMIS, we identified a list of tomato genes with exodermis-specific expression pattern and investigated a number of these genes for their role in exodermis development, namely the role in barrier establishment through suberin and lignin deposition. We found that many of the identified genes were important for exodermis barrier establishment. We tested the role of these genes in response to a drought cue, and found that they were upregulated by drought, and thus they are the likely molecular mechanism that leads to drought-induced exodermis suberin deposition. We started the experiments to identify the regulatory targets of three candidate transcription factors, but due to Covid-19 this work was delayed and continues as ongoing research.

Key results of the research so far have been published in a high-impact Open Access publication: Kajala et al 2021 (https://doi.org/10.1016/j.cell.2021.04.024) and presented at four international conferences, three Dutch conferences, and four invited seminars at European universities.

Additionally, a review on convergent evolution of drought protective traits, such as exodermis barriers, was written as part of TOMATO EXODERMIS (https://doi.org/10.1111/pce.14143).
TOMATO EXODERMIS has contributed to the progress beyond the state-of-the-art understanding of cell type-specific gene expression patterns and their regulation (https://doi.org/10.1016/j.cell.2021.04.024). Methodological advancement in RNAseq library construction have been published in Bjornson et al (https://doi.org/10.21769/BioProtoc.3799).

TOMATO EXODERMIS had impact to the career of the early career researcher Dr. Kajala. Firstly, TOMATO EXODERMIS enabled establishment of the exodermis research line in the Kajala lab at Utrecht University. This foundation was a key for the success of NWO-VIDI proposal on exodermis evolution, and Kajala lab being integrated into the European Suberin Network.

The long-term wider socio-economic and social implications of TOMATO EXODERMIS revolve around production of climate-resilient crops. Understanding the underpinnings of exodermal barriers allows targeting them for breeding, and many European field crops, such as tomato itself, but also closely related potato, eggplant and peppers can apply this genetic knowledge. Field crops with more responsive and effective exodermis barriers would be better protected against drought, salinity, heavy metals and flooding and provide more stable food supply.
Tomato exodermal suberin accumulates in drought