Abstract
The plant cell wall acts not only as a physical barrier, but also as a complex and dynamic structure that actively changes under different biotic and abiotic stress conditions. The question is, how are the different cell wall compounds modified during different interactions with exogenous stimuli such as pathogens? Plants exposed to viral pathogens respond to unfavorable conditions on multiple levels. One challenge that plants face under viral stress is the number of processes required for differential cell wall remodeling. The key players in these conditions are the cell wall genes and proteins, which can be regulated in specific ways during the interactions and have direct influences on the rebuilding of the cell wall structure. The cell wall modifications occurring in plants during viral infection remain poorly described. Therefore, this study focuses on cell wall dynamics as an effect of incompatible interactions between the potato virus Y (PVYNTN) and resistant potatoes (hypersensitive plant), as well as compatible (susceptible plant) interactions. Our analysis describes, for the first time, the expression of the potato expansin A3 (StEXPA3) and potato extensin 4 (StEXT4) genes in PVYNTN-susceptible and -resistant potato plant interactions. The results indicated a statistically significant induction of the StEXPA3 gene during a susceptible response. By contrast, we demonstrated the predominantly gradual activation of the StEXT4 gene during the hypersensitive response to PVYNTN inoculation. Moreover, the in situ distributions of expansins (StEXPAs), which are essential cell wall-associated proteins, and the hydroxyproline-rich glycoprotein (HRGP) extensin were investigated in two types of interactions. Furthermore, cell wall loosening was accompanied by an increase in StEXPA deposition in a PVYNTN-susceptible potato, whereas the HRGP content dynamically increased during the hypersensitive response, when the cell wall was reinforced. Ultrastructural localization and quantification revealed that the HRGP extensin was preferably located in the apoplast, but deposition in the symplast was also observed in resistant plants. Interestingly, during the hypersensitive response, StEXPA proteins were mainly located in the symplast area, in contrast to the susceptible potato where StEXPA proteins were mainly observed in the cell wall. These findings revealed that changes in the intracellular distribution and abundance of StEXPAs and HRGPs can be differentially regulated, depending on different types of PVYNTN–potato plant interactions, and confirmed the involvement of apoplast and symplast activation as a defense response mechanism.
Highlights
The plant cell wall operates as a complex structure with a diversity of functions throughout the whole plant life
Cell wall loosening was accompanied by an increase in situ distributions of expansins (StEXPAs) deposition in a PVYNTN -susceptible potato, whereas the hydroxyproline-rich glycoprotein (HRGP) content dynamically increased during the hypersensitive response, when the cell wall was reinforced
We demonstrated that PVYNTN inoculation affected StEXPA3 and StEXT4 expression in both types of interactions
Summary
The plant cell wall operates as a complex structure with a diversity of functions throughout the whole plant life. Through the action of many structural components, which are necessary for plant growth and acclimatization in the environment, the plant cell wall is a place of constant assembly, remodeling, or disassembly processes during the lifetime of the plant [1]. Consistent with its role in different processes, the plant cell wall structure can dynamically change, between different plant species, and between different tissue types [2]. As postulated by Tucker and Koltunow [3], a dynamic primary wall is established in young cells during division and provides flexibility and structural support. The plant cell wall may act as a passive structural barrier as well as establish active induced defense [5]. Genes encoding proteins and/or enzymes capable of synthesizing or hydrolyzing components of the plant cell wall display different expressions or activities under different stress conditions, suggesting that they have roles in enabling stress tolerance through changes in the cell wall composition
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