Outer root layer controls twisted root growth ^{CEFR B2}

Researchers led by Ram Dixit at Washington University in St. Louis, with Natasha Nolan and engineer Guy Genin and co-senior author Charles Anderson, studied how roots develop their twisted growth. Their study in Nature Communications, produced within the NSF-funded Center for Engineering Mechanobiology (CEMB), asked whether twisting requires a full loss of gene function or only a localized change in gene expression.

In a model plant system whose roots skew right or left, the team expressed the wild-type version of a key gene in particular cell layers. They found that restoring the gene in inner layers left the plants twisted, as if the mutation still dominated. In contrast, expressing the same gene only in the epidermis—the outer cell layer—restored straight root growth. That result shows the epidermis can mechanically coordinate growth across the whole organ.

Mechanobiology measurements and computer modelling clarified the mechanism. Anderson’s lab measured shifts in the orientation of cellulose microfibrils in mutant roots, and Genin’s model showed concentric layers behave like rings in a trunk: the outer ring has more leverage. "The outer layer rules," he said. The model suggested that skew in the epidermis can produce about one-third of the twist seen if every layer is skewed, and that straightening the epidermis can straighten the entire root. Dixit summarised: "the epidermis is not a passive skin, but instead a mechanical coordinator of the growth of the entire organ." The authors suggest these findings provide targets and a mechanical framework for engineering root architecture, which could help crops as drought and poor soils become more common. The study was supported by CEMB (NSF) and the National Institute of General Medical Sciences (NIH). Source: Washington University in St. Louis.