# Insights into widespread disturbance in gene expression and severe growth inhibition observed in transgenic rice producing polyhydroxybutyrate

## TL;DR

Transgenic rice producing PHB experiences severe growth issues due to gene expression disturbances caused by the phaC gene.

## Contribution

The study identifies the phaC gene as a key driver of gene expression disturbances and growth inhibition in PHB-producing rice.

## Key findings

- PHB accumulation in transgenic rice causes severe growth inhibition and early-stage death.
- The phaC gene significantly alters gene expression, especially in stress response and cellular processes.
- Microarray analysis shows that phaC gene expression disrupts multiple cell functions, leading to cell death.

## Abstract

Production of polyhydroxybutyrate (PHB), a kind of biodegradable polymer, was attempted using transformant rice, in which the genes involved in PHB biosynthesis in Cupriavidus necator were introduced. Accumulation of PHB was observed in the transformants containing the genes for β-ketothiolase (phaA), acetoacetyl-CoA reductase (phaB) and PHB synthase (phaC) (PhaABC lines) and those containing phaB and phaC (PhaBC lines). However, they immediately withered after regeneration due to severe growth inhibition, whereas no growth inhibition occurred in the PhaAB lines containing phaA and phaB, and the PhaC lines containing phaC, which did not produce PHB. Crossing between them generated sufficient quantities of F1 seeds. Many of them germinated and produced PHB, but they died at an early stage of growth. This suggests that the accumulation of PHB in the cells caused a strong growth inhibition. Microarray analysis using the PhaBC and PhaC lines revealed very similar expression profiles, suggesting that most of the changes in gene expression were mainly caused by phaC gene expression. PhaC transformants exhibited increased expression of genes involved in the stress response, certain biological processes and cellular components. These results strongly suggest that phaC gene expression results in perturbation of gene expression levels in various cell functions. It was concluded that the disturbance of cell function caused by phaC gene expression is enhanced by the intracellular production of PHB, leading to cell death.