The Growing World of Expansins

Abstract

Expansins are cell wall proteins that induce pH-dependent wall extension and stress relaxation in a characteristic and unique manner. Two families of expansins are known, named alpha- and beta-expansins, and they comprise large multigene families whose members show diverse organ-, tissue- and cell-specific expression patterns. Other genes that bear distant sequence similarity to expansins are also represented in the sequence databases, but their biological and biochemical functions have not yet been uncovered. Expansin appears to weaken glucan-glucan binding, but its detailed mechanism of action is not well established. The biological roles of expansins are diverse, but can be related to the action of expansins to loosen cell walls, for example during cell enlargement, fruit softening, pollen tube and root hair growth, and abscission. Expansin-like proteins have also been identified in bacteria and fungi, where they may aid microbial invasion of the plant body.

Isolation, Characterization, and Pericycle-Specific Transcriptome Analyses of the Novel Maize Lateral and Seminal Root Initiation Mutant rum1

“…This might explain why stress-and cell-wall-related genes that facilitate water and nutrient uptake by modifying the chemical composition of the cell wall are preferentially expressed in the mutant rum1. Expansins are, for example, cell wall proteins that induce pH-dependent wall extension and stress relaxation to loosen cell walls during cell enlargement and root hair growth (Cosgrove et al, 2002). A similar up-regulation of genes involved in lignin biosynthesis, e.g.…”

Genome-Wide Association Mapping of Fertility Reduction upon Heat Stress Reveals Developmental Stage-Specific QTLs in Arabidopsis thaliana

“…These five SNPs are located in the promoter of AT3G45970, 1.2 kb upstream of the start codon, and are in low LD (0.2 < LD < 0.4) with SNPs in the gene AT3G45960 (Supplemental Figure 1). Both genes are annotated as expansinlike A and are suggested to be involved in cell wall loosening (Cosgrove et al, 2002). The significant SNP of QTL7 is located in a large linkage block starting 43 kb upstream and ending 76 kb downstream of the significant SNP.…”

Infection and Invasion of Roots by Symbiotic, Nitrogen-Fixing Rhizobia during Nodulation of Temperate Legumes

“…During growth in the rhizosphere of a host plant, rhizobia sense compounds such as flavonoids and betaines secreted by the host root and respond by inducing nod genes (29,35,34). The nod genes encode approximately 25 proteins required for the bacterial synthesis and export of Nod factor.…”

“…It should be noted that electron micrographs depicting the degradation associated specifically with infection thread initiation show that degradation, while localized, is more widespread and diffuse than that shown by Mateos et al Plants clearly have the capability to degrade, or otherwise alter, their cell walls. For example, cell walls are weakened or degraded during root hair initiation, fruit ripening, pollen tube transit down the pistil, and leaf abscission (21,34,35,137). Observations that cell wall-degrading enzyme activities, induced by compatible bacteria, do not occur in the presence of nitrate are easiest to explain if the host has at least some control over degradation in response to rhizobial infection (52,105,173).…”