OsBIC1 Directly Interacts with OsCRYs to Regulate Leaf Sheath Length through Mediating GA-Responsive Pathway

Area of Science:

• Plant molecular biology
• Photobiology
• Plant development

Background:

• Cryptochromes (CRY1 and CRY2) are blue light receptors regulating key processes in *Arabidopsis thaliana*.
• Blue-light Inhibitor of Cryptochrome 1 and 2 (BIC1 and BIC2) interact with CRY proteins, with BIC1 suppressing CRY2 activity in *Arabidopsis*.
• The function of BIC proteins in crops, particularly rice (*Oryza sativa*), remains largely uncharacterized.

Purpose of the Study:

• To identify and functionally characterize rice homologs of *Arabidopsis* BIC1 and BIC2 (*OsBIC1* and *OsBIC2*).
• To investigate the role of OsBIC1 in regulating blue light responses, specifically leaf sheath elongation.
• To elucidate the interaction between OsBIC1 and rice cryptochromes (OsCRYs) in controlling plant development.

Main Methods:

• Identification of *OsBIC1* and *OsBIC2* genes in rice.
• Analysis of leaf sheath length in *OsBIC1* and *OsBIC2* overexpression lines and *OsBIC1* mutants under varying blue light conditions.
• Investigation of OsBIC1-OsCRY interactions using molecular assays.
• Microscopic analysis of leaf sheath epidermal cells.
• RNA-sequencing (RNA-seq) and quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) to analyze gene expression related to the Gibberellic Acid (GA) pathway.

Main Results:

• Overexpression of *OsBIC1* and *OsBIC2* increased rice leaf sheath length.
• Mutations in *OsBIC1* resulted in shorter leaf sheaths, dependent on blue light intensity.
• OsBIC1 directly interacts with OsCRY1a, OsCRY1b, and OsCRY2 (OsCRYs).
• OsBIC1 and OsCRYs regulate leaf sheath length by modulating the ratio of epidermal cell lengths.
• Transcriptome analysis revealed that OsBIC1 and OsCRYs coordinately regulate the GA-responsive pathway.

Conclusions:

• OsBIC1 and OsCRYs function together in rice to regulate blue light-induced leaf sheath elongation.
• The OsBIC1-OsCRYs complex controls leaf sheath elongation by influencing epidermal cell elongation.
• The Gibberellic Acid-responsive pathway is a key molecular mechanism mediating this blue light response.