Arabinogalactan proteins: actors or spectators during abiotic and biotic stress in plants?

Abstract

Arabinogalactan proteins (AGPs) are a family of hydroxyproline-rich glycoproteins (HRGP) ubiquitous in the plant kingdom. They are probably one of the most heterogeneous and complex families of macromolecules, making them able to perform different and multiple functions. Located at the plasma membrane-cell wall interface, AGPs are involved in several processes, from plant growth and development to reproduction. An additional function of AGPs in response to biotic and abiotic stress has been suggested by several studies. The purpose of this review is to summarize critically and analytically the available knowledge on the effects of abiotic stress (low and high temperatures, drought, flooding, anoxia and metal deficiency/toxicity) and biotic stress (bacteria, fungi, nematodes and viruses) on AGPs. A deeper understanding of the role of AGPs during these conditions can be an important tool for understanding AGP biology and for the possible development of efficient breeding strategies.

Plant Cell Walls Tackling Climate Change: Biotechnological Strategies to Improve Crop Adaptations and Photosynthesis in Response to Global Warming

“…The release of different AGPs has been considered as an efficient response mechanism to salt stress in plants [124,125]. The involvement of AGPs in salt stress has been linked to the role of AGPs in controlling cell expansion.…”

“…On the contrary, non-adapted tobacco cells showed high levels of AGPs on the plasma membrane [129,130] and an upregulation of AGPs in tobacco cells exposed to salt stress [68]. The role of AGPs expands, during salt stress, from an increase in the stiffness of the CW (when AGPs decrease), to the activation of signaling mechanisms by releasing extracellular AGPs, or to the accumulation of soluble sugars in the cytoplasm to decrease water loss [119,125]. The fasciclin-like arabinogalactan-proteins (FLAs) are members of the super-large family of arabinogalactan-proteins (AGPs).…”

“…An increase in the accumulation of these proteins helps preserve proper water levels in the wall in order to facilitate an optimal CW mechanical integrity in case the water levels fall below a certain critical level. This reorganization could also be implicated in the occurrence of a resistance mechanism, whereas the creation of a "buffer zone" prevents the direct interaction between membranes and CW matrix [125]. In rice, expression studies have shown that the expression of several AGPs such as OsAGP1, OsAGP15, and OsELA3 was induced, in response to drought [179].…”

“…In reproductive organs, the expression of AGPs was downregulated mainly in the stigmas and ovules in tomato plants (S. lycopersicum cv. Micro-Tom) [124,125]. In stems and reproductive tissues that are not directly exposed to atmospheric conditions, it has been suggested that AGP expression is downregulated to save more energy.…”

“…In stems and reproductive tissues that are not directly exposed to atmospheric conditions, it has been suggested that AGP expression is downregulated to save more energy. However, in leaf tissues, which are more susceptible to water loss, AGP contents increase accompanying an increase in the epidermal CW thickness which would limit further water loss caused by heat stress [124,125]. Overall, currently, the main CW factors (from transcriptional and post-transcriptional regulating factors, to the single enzymes involved) that contribute to the activation of plant thermotolerance remain largely unknown in most plant species, and therefore further investigation is required.…”