Epsilon Archive for Student Projects

Abstract

Potato (Solanum tuberosum) is an important crop for food security, but cultivation is threatened by
various disease and abiotic stresses that could increase with climate change. To reduce fungicide
use, plant breeding approaches implementing knock-out of susceptibility genes (S-genes) are of
growing interest. S-genes are generally more robust than R-genes and can confer broad-spectrum
disease resistance and abiotic stress tolerance. In this study, two S-genes are investigated for their
molecular and physiological function.
The S-gene CHL1 contains a putative cryptochrome-interacting domain, which is suggested to be
involved in regulation of photosynthetic pigment synthesis in response to UV light. Samples from a
field trial were found to have increased levels of photosynthetic pigments in chl1 mutants, and
transcript abundance of genes in the chlorophyll synthesis pathway has been analyzed. The
phenotype was not possible to reproduce in vitro, under strong UV light. The suggested interaction
with cryptochrome and potential regulation of chlorophyll synthesis is not excluded and could be
dependent on interactions of additional factors that were present in the field.
The S-gene DMR6-1 is involved in catabolism of the phytohormone salicylic acid (SA), which is
induced both during biotic and abiotic stress. Plant growth during controlled conditions with 60 mM
NaCl was shown to be increased in mutant lines. During growth in soil with 100 mM NaCl the
mutants showed increased levels of chlorophyll, indicating better tolerance to the salt-induced stress.
Analysis on transcriptional activity of marker genes in respective pathways for SA, ethylene, and
proline, did not indicate any significant differences. However, a slight trend of increased mRNA
abundance could be seen, especially for the SA marker PR1, in both saline stress and control
conditions, indicating the function of the mutant.
The double mutant of both chl1 and dmr6-1 was evaluated for resistance against Phytophthora
infestans in a detached leaf assay, where resistance levels were found to be consistent with the single
dmr6-1 mutants and no additive resistance was conferred.