Endogenous rhythmic growth in oak trees is regulated by internal clocks rather than resource availability

Area of Science:

• Plant Biology
• Ecology
• Molecular Biology

Background:

• Common oak trees (Quercus robur L.) exhibit endogenous rhythmic growth with alternating shoot and root flushes.
• Understanding the underlying mechanisms of this rhythmic growth is crucial for plant science.

Purpose of the Study:

• To investigate the mechanisms governing rhythmic growth in oak trees.
• To determine the effect of ectomycorrhizal fungus Piloderma croceum on rhythmic growth and resource allocation.

Main Methods:

• Utilized (13)C/(15)N labeling and RNA sequencing (RNASeq) transcript profiling on oak microcuttings.
• Assessed the impact of P. croceum inoculation on plant internal resource availability and growth patterns.
• Analyzed differentially expressed genes (DEGs) and Gene Ontology (GO) terms during growth cessation.

Main Results:

• Rhythmic growth correlated with shifts in above- and below-ground carbon and nitrogen allocation.
• P. croceum inoculation enhanced plant growth but did not alter rhythmic growth or resource allocation patterns.
• Two distinct shifts in transcript abundance were observed during root and shoot growth cessation, primarily involving down-regulated genes.
• P. croceum suppressed transcript shifts in roots but not in shoots.

Conclusions:

• Rhythmic growth in oaks involves significant oscillations in plant metabolism and gene regulation between above- and below-ground parts.
• Genes related to signaling and circadian clock regulation were identified as potentially core processes governing rhythmic growth.
• Ectomycorrhizal symbiosis may play a role in moderating these oscillations without changing the fundamental rhythmic growth pattern.