Interaction of abiotic stress in the root zone on resistance- and defence associated responses in the leaf

authored by

Helena Sophia Domes

supervised by

Thomas Debener

Abstract

In nature, plants are exposed to a multitude of stresses simultaneously. In order to gain a deeper understanding of the interaction between abiotic phosphorus deficiency and biotic fungal infection of leaves, a detailed investigation was conducted on roses. The fungal pathogens selected for study were the ascomycetes Diplocarpon rosae, responsible for black spot disease, and Podosphaera pannosa, causing powdery mildew, which are both highly prevalent in rose cultivation worldwide. Although the interaction of roses with these two pathogens is of great economic importance, it is still not fully understood. Furthermore, the molecular pathways of the defence reaction remain unclear, and the impact of phosphorus deficiency is also unknown. RNA-Seq data were employed to investigate the transcriptomic response of the susceptible rose variety ‘Pariser Charme’ (PC) to inoculation with P. pannosa and D. rosae. In response to inoculation with P. pannosa, genes related to photosynthesis and cell wall modification are down-regulated, whereas genes from the phenylpropanoid and flavonoid pathways, as well as those of the salicylic acid-signalling pathway, are specifically up-regulated in response to D. rosae. As a first indication of a crosstalk between phosphate starvation signalling and defence responses, the differential regulation of phosphate transporters was observed in RNA-Seq and RT-qPCR data from rose leaves inoculated with D. rosae or P. pannosa (susceptible: PC; resistant to D. rosae: PC::Rdr1 and 91/100-5). The resistance status did not influence the outcome, but there were differences depending on the fungus. Furthermore, the impact of phosphate deficiency on black spot disease and gene expression in rose leaves was investigated in six genotypes of the 97/7 population, which encompasses both resistant and susceptible genotypes. Gene expression exhibited pronounced genotypic effects, despite the close relationship within the population. However, no consistent pattern of expression changes of defence related genes could be detected with combined stress compared to individually applied stress. Our microscopic data and the quantification of fungal biomass by ITS-PCR also demonstrate that phosphate deficiency does not affect susceptibility. This indicates that, although it affects the gene expression of pathogen-responsive genes in some genotypes, Pi starvation does not significantly affect the colonisation with D. rosae in roses. The analysis of six rose genomes led to the identification of 68 putative members of the WRKY transcription factor family, which play a crucial role in plant regulatory networks. Transcriptomic profiling of three rose genotypes inoculated with D. rosae revealed differential regulation of WRKY genes. Given its documented role in phosphate signalling and induction following inoculation with D. rosae, RcWRKY37, a homolog of AtWRKY75 and FaWRKY1, was subjected to further investigation. However, its overexpression did not result in the expression of phosphate transporters or defence-related genes. Therefore, RcWRKY37 cannot be considered as a point of overlap between Pi starvation and defence response signalling against D. rosae.

Organisation(s)

Section Molecular Plant Breeding
Institute of Plant Genetics

Type

Doctoral thesis

No. of pages

100

Publication date

30.10.2024

Publication status

Published

Electronic version(s)

https://doi.org/10.15488/18092 (Access: Open)