Differential expression of oxygen-evolving polypeptide genes in maize leaf cell types.

Area of Science:

• Plant Biology
• Photosynthesis Research
• Molecular Biology

Background:

• Photosystem II (PSII) is crucial for oxygenic photosynthesis.
• The oxygen-evolving (OE) complex within PSII facilitates water splitting.
• Understanding the regulation of OE proteins is key to optimizing photosynthetic efficiency.

Purpose of the Study:

• To investigate the cellular localization and regulation of three OE polypeptides (33 kD, 23 kD, 16 kD) in maize.
• To determine the roles of transcriptional and translational control in OE protein abundance.
• To compare OE protein expression in mesophyll and bundle sheath cells.

Main Methods:

• Alkaline Tris treatment to release OE polypeptides from maize PSII particles.
• Cross-reactivity assays using antisera against spinach OE polypeptides.
• Identification of maize cDNA clones (OE33, OE23, OE16) via hybrid-selection, in vitro translation, and immunoprecipitation.
• Analysis of transcript and protein levels in etiolated, greening, and green leaves.

Main Results:

• Three OE polypeptides (33, 23, 16 kD) were identified in maize, cross-reacting with spinach OE antisera.
• These OE proteins are approximately four times more abundant in mesophyll than bundle sheath cells.
• Transcripts for OE genes are present in both cell types but accumulate transiently in mesophyll cells upon illumination.
• Protein levels increase in mesophyll cells during greening, correlating with transcript accumulation.
• Light stimulates OE protein accumulation in bundle sheath cells independently of mRNA levels.

Conclusions:

• Preferential localization of OE proteins in maize mesophyll cells is regulated at both transcriptional and translational levels.
• Light plays a significant role in regulating OE protein abundance in both cell types.
• Differential gene expression and post-transcriptional regulation contribute to the spatial distribution of OE proteins in maize leaves.