Evolution of the C4 phosphoenolpyruvate carboxylase promoter of the C4 species Flaveria trinervia: the role of the proximal promoter region

Sascha Engelmann,Peter Westhoff,Corinna Zogel,Monika Streubel,Maria Koczor,Ute Schlue

doi:10.1186/1471-2229-8-4

Abstract

BackgroundThe key enzymes of photosynthetic carbon assimilation in C4 plants have evolved independently several times from C3 isoforms that were present in the C3 ancestral species. The C4 isoform of phosphoenolpyruvate carboxylase (PEPC), the primary CO2-fixing enzyme of the C4 cycle, is specifically expressed at high levels in mesophyll cells of the leaves of C4 species. We are interested in understanding the molecular changes that are responsible for the evolution of this C4-characteristic PEPC expression pattern, and we are using the genus Flaveria (Asteraceae) as a model system. It is known that cis-regulatory sequences for mesophyll-specific expression of the ppcA1 gene of F. trinervia (C4) are located within a distal promoter region (DR).ResultsIn this study we focus on the proximal region (PR) of the ppcA1 promoter of F. trinervia and present an analysis of its function in establishing a C4-specific expression pattern. We demonstrate that the PR harbours cis-regulatory determinants which account for high levels of PEPC expression in the leaf. Our results further suggest that an intron in the 5' untranslated leader region of the PR is not essential for the control of ppcA1 gene expression.ConclusionThe allocation of cis-regulatory elements for enhanced expression levels to the proximal region of the ppcA1 promoter provides further insight into the regulation of PEPC expression in C4 leaves.

Highlights

The key enzymes of photosynthetic carbon assimilation in C4 plants have evolved independently several times from C3 isoforms that were present in the C3 ancestral species
Experimental strategy We are interested in elucidating the molecular events that are crucial for the evolution of the high and mesophyllspecific expression of the C4 phosphoenolpyruvate carboxylase gene of the C4 plant F. trinervia
In this study we focus on the proximal promoter region (PR) of the ppcA1 gene with respect to its function in establishing the C4-characteristic expression pattern

Summary

Introduction

The key enzymes of photosynthetic carbon assimilation in C4 plants have evolved independently several times from C3 isoforms that were present in the C3 ancestral species. The C4 isoform of phosphoenolpyruvate carboxylase (PEPC), the primary CO2-fixing enzyme of the C4 cycle, is expressed at high levels in mesophyll cells of the leaves of C4 species. Phosphoenolpyruvate carboxylase (PEPC), which serves as the actual CO2 pump of the C4 pathway, is expressed in the mesophyll cells of C4 leaves. This enzyme is not an unique feature of C4 species; other PEPC isoforms with different catalytic and regulatory properties are found in both photosynthetic and non-photosynthetic tissues of all plants where they participate in a variety of metabolic processes, e.g. replenishment of citric acid cycle intermediates and regulation of guard cell movement [3]

Methods

Results

Conclusion