Effect of Low Red-to-Far-Red Light on Stem Elongation and Pith Cell Development in Dicots

Area of Science:

• Plant Biology
• Plant Physiology
• Molecular Biology

Background:

• Light availability is crucial for plant growth, with dense canopies limiting light penetration.
• The shade avoidance syndrome (SAS) is a plant response to neighbor cues, primarily mediated by changes in light quality, specifically an increase in far-red (FR) light and a low red:far-red light ratio (R:FR).
• While SAS is known to induce internode elongation in tomato, the specific roles of different cell types in this response are not well understood.

Purpose of the Study:

• To characterize the cellular anatomical changes in tomato internodes under low R:FR conditions.
• To investigate the gene expression patterns associated with low R:FR treatment in both whole internodes and dissected pith tissues.
• To explore the conservation of FR responses and associated gene expression in other dicotyledonous species.

Main Methods:

• Tomato plants were subjected to low R:FR light treatments.
• Cellular anatomy of internodes was analyzed, focusing on pith traits.
• Transcriptome profiling was performed on whole internodes and hand-dissected pith tissues.
• FR responses and gene expression were characterized in eight dicot species.

Main Results:

• Low R:FR treatment induced significant changes in tomato pith anatomy, including increased pith layer number, cell diameter, and longitudinal cell length.
• Transcriptome analysis revealed upregulation of specific transcription factors (GATA, TCP, bZIPs) in the central cylinder pith under low R:FR, distinct from whole internode patterns.
• Pith elongation in response to FR light was observed in species with strong internode elongation, and the expression of certain FR-responsive TFs in the pith was conserved within the Solanaceae family.

Conclusions:

• The study identified distinct gene expression patterns in the central cylinder of tomato internodes during SAS, suggesting cell-type-specific responses, likely involving vascular tissues like the pith.
• The observed FR-responsive gene expression patterns in the pith are conserved in close relatives of tomato but not broadly across other dicot families.
• These findings indicate that molecular mechanisms underlying FR responses can vary significantly among different dicot species.