Strigolactones Play an Important Role in Shaping Exodermal Morphology via a KAI2-Dependent Pathway

Area of Science:

• Plant Biology
• Root Development
• Plant Physiology

Background:

• Land plants possess two suberized root barriers: the endodermis and hypodermis (exodermis).
• Passage cells within these barriers are crucial for regulating water and nutrient transport between roots and soil.
• Knowledge regarding hypodermal passage cells (HPCs) and their regulation remains limited compared to endodermal passage cells.

Purpose of the Study:

• To investigate the factors regulating the number of hypodermal passage cells (HPCs) in Petunia roots.
• To elucidate the roles of plant hormones and signaling pathways in HPC development.

Main Methods:

• Hormonal treatments applied to Petunia roots to observe effects on HPC number.
• Analysis of HPC numbers in various Petunia mutants, including strigolactone signaling (d14/dad2, max2) and karrikin signaling (KAI2) mutants.
• Genetic analysis to identify key receptors involved in HPC regulation.

Main Results:

• Strigolactones positively influence HPC number, while abscisic acid (ABA), ethylene, and auxin significantly reduce it.
• Strigolactone signaling mutants (d14/dad2) exhibited increased HPC numbers, whereas the max2 mutant showed decreased HPC numbers.
• Mutations in the karrikin sensor KAI2 drastically reduced HPC amounts, indicating the KAI2/MAX2 receptor complex is central to HPC number determination.

Conclusions:

• Hormonal signaling pathways, particularly those involving strigolactones, ABA, ethylene, and auxin, play critical roles in regulating HPC formation in Petunia.
• The dimeric KAI2/MAX2 receptor complex is identified as a key regulator of HPC number, highlighting its importance in root barrier development.