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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

13.4 DEFENSE-RELATED PROTEINS IN PLANT CELL ORGANELLES

Abiotic stress causes a wide range of alterations in protein expression levels

in plant cells. There is no direct relationship between gene expression and

the end outcome of protein synthesis and regulation. The presence of a

specific protein in a cell does not always imply an increase or reduction

in gene expression. Protein expression is governed by several mechanisms,

including protein targeting and translocation, as well as post-translational

modifications, which are all influenced by stress. Secretory mechanisms and

intracellular interactions regulate protein distribution in the cell. When plants

are exposed to abiotic stress, they frequently regulate groups of functionally

related proteins. Some of these proteins are not involved in the defensive

system, but those involved in metabolism, storage, and protein synthesis.

According to their roles, defense-related abiotic stress-responsive proteins

were classified into six major groups (Lilley et al., 2007; Hossain et al.,

2012). These six differentially expressed proteins strongly combat repairing

the negative effects of abiotic stress which includes protein misfolding or

aggregation, ROS production, ion imbalance, and osmotic potential in plant

cell organelles (Figure 13.2).

13.4.1 PROTEOLYTIC PROTEINS

Proteolysis is a process in which misfolded, unassembled, or mutant proteins

were degraded in cells. Among all the organelles ER contains its proteo­

lytic system, which is responsible for protein folding and quality control.

Although ubiquitin was generally involved in protein breakdown, proteolysis

without ubiquitin is conceivable (Tanaka & Chiba, 1998). The ER degrada­

tion machinery’s ubiquitin-proteasome system has been discovered to extend

into the cytoplasm. The ubiquitin-protein degradation mechanisms have also

been discovered in the nucleus (Sommer & Wolf, 1997). Two types of stress-

responsive proteins that interact directly with target proteins include proteo­

lytic proteins and molecular chaperones. Proteolysis-related protein activity

might be thought of as the cell’s final effort to survive in stressful situations.

Organelles are designed to work together with other compartments to carry

out cellular activities (Hieng et al., 2004).

13.4.2 CHAPERONE PROTEINS

Chaperone proteins are found in nearly every region of a cell participate

in the correct protein folding and assembly of secretory proteins (Cascardo