# Thai Oakleaf Lettuce Phenocopies a Phytochrome B Mutant

## TL;DR

Thai Oakleaf lettuce behaves like a plant with a broken phytochrome B, affecting how it responds to red light and heat.

## Contribution

Thai Oakleaf lettuce is identified as a natural phenocopy of a phytochrome B mutant in red-light and thermosensing.

## Key findings

- Thai Oakleaf lettuce shows defects in red-light mediated hypocotyl growth inhibition.
- The lettuce variety exhibits decreased cotyledon expansion and shade avoidance under red light.
- Its heat tolerance aligns with phytochrome B's role as a thermosensor.

## Abstract

Lettuce is an important crop in indoor production (“vertical farming”) systems. In the current study, seedling growth habits were analyzed to make predictions about mature plant growth and development under narrow bandwidth light. We show that the lettuce variety Thai Oakleaf demonstrates defects in normal red-light-mediated development, which is reminiscent of mutations in a central red light photosensory pathway.

Photomorphogenic development in seedlings may be diagnostic of future plant performance. In this report, we characterize the Thai Oakleaf lettuce genotype, as it exhibited abnormalities in photomorphogenic development that were the most conspicuous under red light, including defects in hypocotyl growth inhibition, decreased cotyledon expansion, and constitutive shade avoidance tendencies. These observations are consistent with defects in red light sensing through the phytochrome B (phyB) photoreceptor system. This genotype is sold commercially as a heat-tolerant variety, which aligns with the evidence that phyB acts as a thermosensor.