Functional Divergence of Plant Expansins as Revealed by Genetic Complementation of Root-Hair Tip Growth in Arabidopsis Thaliana

This study investigates the role of expansins in root hair tip growth in Arabidopsis thaliana by using CRISPR/Cas9 to knock out specific α-expansins, EXPA7 and EXPA18, which halted root hair elongation. Complementation with various expansin genes revealed functional differences, with some genes fully restoring growth, while others did not, particularly those lacking a conserved Asp residue essential for wall enlargement. Phylogenetic analysis suggests the loss of this Asp occurred before the evolution of angiosperms. The study highlights the functional diversity among expansin families and clades, demonstrating that differences in protein trafficking, wall binding, and evolutionary changes contribute to their varied roles in plant growth.