Regional Growth Rate Differences Specified by Apical Notch Activities Regulate Liverwort Thallus Shape

Area of Science:

• Plant morphology and developmental biology
• Evolutionary developmental biology
• Computational biology

Background:

• Liverworts, the most ancient land plant lineage, possess a flattened thallus body shape.
• The genetic mechanisms governing liverwort thallus shape are largely unknown.
• Understanding liverwort development offers insights into the evolution of plant forms.

Purpose of the Study:

• To investigate the regulatory mechanisms controlling liverwort thallus shape in Marchantia polymorpha.
• To differentiate between competing models of growth regulation in liverworts.

Main Methods:

• Live imaging of plant growth.
• Quantitative growth analyses.
• Computational modeling and simulations.
• Surgical experiments involving notch excision.

Main Results:

• Marchantia polymorpha thallus shape follows a predictable sequence of transitions in early growth.
• Regional growth rate differences, driven by apical notches, are crucial for overall thallus shape.
• A "notch-pre-patterns-growth" model, where growth regulators are pre-patterned by notches, aligns better with experimental data than a "notch-drives-growth" model.
• Persistent growth after notch excision indicates limitations of the "notch-drives-growth" model.

Conclusions:

• Growth rate heterogeneity is the primary determinant of Marchantia polymorpha thallus shape.
• The findings suggest the existence of specialized functional zones within the liverwort thallus.
• The study provides a framework for understanding the genetic basis of plant body plan evolution.