Abstract
Two apple rootstock genotypes G.935 and B.9 were recently demonstrated to exhibit distinct resistance responses following infection by Pythium ultimum. As part of an effort to elucidate the genetic regulation of apple root resistance to soilborne pathogens, preinoculation transcriptome variations in roots of these two apple rootstock genotypes are hypothesized to contribute to the observed disease resistance phenotypes. Results from current comparative transcriptome analysis demonstrated elevated transcript abundance for many genes which function in a system-wide defense response in the root tissue of the resistant genotype of G.935 in comparison with susceptible B.9. Based on the functional annotation, these differentially expressed genes encode proteins that function in several tiers of defense responses, such as pattern recognition receptors for pathogen detection and subsequent signal transduction, defense hormone biosynthesis and signaling, transcription factors with known roles in defense activation, enzymes of secondary metabolism, and various classes of resistance proteins. The data set suggested a more poised status, which is ready to defend pathogen infection, in the root tissues of resistant genotype of G.935, compared to the susceptible B.9. The significance of preformed defense in the absence of a pathogen toward overall resistance phenotypes in apple root and the potential fitness cost due to the overactivated defense system were discussed.
Highlights
During their coevolution with pathogens, plants developed a sophisticated, two-layered innate immune system that confers resistance against most microbial pathogens [1,2,3]
The first line of defense is initiated upon perception of a conserved pathogen-associated molecular pattern (PAMP) by pattern recognition receptor (PRR) embedded in the plant’s plasma membrane, activating so-called PAMP-triggered immunity (PTI)
Log2FC values of 2 and greater were used as the criteria for differentially expressed gene (DEG) identification, and about 3.01% of all predicted genes in apple genome were identified as Differentially expressed genes (DEGs) between these two genotypes
Summary
During their coevolution with pathogens, plants developed a sophisticated, two-layered innate immune system that confers resistance against most microbial pathogens [1,2,3]. On the plant side, coevolved resistance (R) genes directly or indirectly detect pathogen virulence effectors and initiate the second layer of defense called effector-triggered immunity (ETI) [1, 7]. The second layer of plant immunity relies on the specific recognition of pathogen effectors by disease resistance proteins (R), leading to a strong and specific immune response toward those isolates of a pathogen that produce the recognized effector. These common responses of plant defense systems occur after the plant encounters a pathogen, but is it possible that in some cases plant defenses are already “primed” before inoculation?
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