OsPEX1, an extensin-like protein, negatively regulates root growth in a gibberellin-mediated manner in rice

Leucine-rich repeat extensins (LRXs) are required for plant growth and development through affecting cell growth and cell wall formation. LRX gene family can be classified into two categories: predominantly vegetative-expressed LRX and reproductive-expressed PEX. In contrast to the tissue specificity of Arabidopsis PEX genes in reproductive organs, rice OsPEX1 are also highly expressed in roots in addition to reproductive tissue. However, whether and how OsPEX1 affects root growth is unclear. Here, we found that overexpression of OsPEX1 in the pex1 mutant retarded root growth by reducing cell elongation resulting from an increase of lignin deposition, whereas knockdown of OsPEX1 had an opposite effect on root growth, indicating that OsPEX1 negatively regulated root growth in rice seedling. Upon further investigation, we uncovered the existence of a feedback loop between OsPEX1 transcription and GA biosynthesis for proper root growth. This was supported by the facts that exogenous GA3 application downregulated the transcription levels of OsPEX1 and lignin-related genes, rescuing the development defects of the root in the pex1 mutant, whereas OsPEX1 negatively regulated GA level by altering the expression of GA biosynthesis genes. Moreover, OsPEX1 and GA showed antagonistic action on the lignin biosynthesis in root. OsPEX1 overexpression upregulated the transcription levels of lignin-related genes, whereas exogenous GA application downregulated their expression, accompanied by altered root growth phenotypes. Taken together, our studies reveal a possible molecular pathway of OsPEX1-mediated root growth through coordinate modulation of lignin deposition via a negative feedback regulation between OsPEX1 transcription and GA biosynthesis.