The SHORT-ROOT-like gene PtSHR2B is involved in Populus phellogen activity

Area of Science:

• Plant molecular biology
• Plant development
• Forest genetics

Background:

• SHORT-ROOT (SHR) is a key transcription factor regulating root development in Arabidopsis thaliana.
• Three SHR-like genes exist in Populus trichocarpa: PtSHR1, PtSHR2A, and PtSHR2B.
• PtSHR1 is similar to Arabidopsis SHR, while PtSHR2A and PtSHR2B have shorter 5' ends.

Purpose of the Study:

• To investigate the function of Populus trichocarpa SHR-like genes, particularly PtSHR2B.
• To understand the role of PtSHR2B in tree growth, bark formation, and hormone regulation.
• To explore the functional diversification of SHR genes in Populus compared to Arabidopsis.

Main Methods:

• Gene expression analysis (promoter:uidA fusions, RT-qPCR).
• Creation and analysis of transgenic hybrid aspen expressing PtSHR2B under a constitutive promoter.
• Hormone quantification using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Main Results:

• PtSHR2B expression was detected in the phellogen, distinct from PtSHR1's cambial zone expression.
• Transgenic trees overexpressing PtSHR2B exhibited reduced overall growth and increased bark proportion.
• Overexpression of PtSHR2B led to elevated cytokinin metabolism and response gene transcripts and increased total cytokinin levels.

Conclusions:

• PtSHR2B plays a role in phellogen regulation, influencing phellem and periderm formation, potentially via cytokinin homeostasis.
• SHR gene function has diversified following the evolutionary split between Populus and Arabidopsis lineages.
• Findings may inform breeding strategies for cork oak, where phellogen activity is crucial for cork production.