Analysis of Global Gene Expression in Maize (Zea mays) Vegetative and Reproductive Tissues That Differ in Accumulation of Starch and Sucrose.

Cristal López-González,C. Gillmor,Sheila Juárez-Colunga,Axel Tiessen,Nayelli Marsch-Martínez,Samuel Trachsel

doi:10.3390/plants11030238

Abstract

Carbon allocation between vegetative and reproductive tissues impacts cereal grain production. Despite great agricultural importance, sink–source relationships have not been fully characterized at the early reproductive stages in maize. Here, we quantify the accumulation of non-structural carbohydrates and patterns of gene expression in the top internode of the stem and the female inflorescence of maize at the onset of grain filling (reproductive stage R1). Top internode stem and female inflorescence tissues of the Puma maize inbred line were collected at reproductive stage R1 (without pollination) and non-structural carbohydrates were quantified by spectrophotometry. The female inflorescence accumulated starch at higher levels than the top internode of the stem. Global mRNA transcript levels were then evaluated in both tissues by RNA sequencing. Gene expression analysis identified 491 genes differentially expressed between the female inflorescence and the top stem internode. Gene ontology classification of differentially expressed genes showed enrichment for sucrose synthesis, the light-dependent reactions of photosynthesis, and transmembrane transporters. Our results suggest that sugar transporters play a key role in sugar partitioning in the maize stem and reveal previously uncharacterized differences between the female inflorescence and the top internode of the stem at early reproductive stages.

Highlights

Yield and harvest indices in cereals are impacted by the partitioning of carbon between vegetative and reproductive tissues
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Carbon partitioning in the maize stem is a dynamic process that takes place between the vegetative and reproductive stages

Summary

Introduction

Yield and harvest indices in cereals are impacted by the partitioning of carbon between vegetative and reproductive tissues. Photoassimilates produced in the source tissues travel through the phloem as sucrose and accumulate in sink tissues as starch [1,2,3]. Source strength is determined by both the rate of photosynthesis and the rate of photoassimilate export from source tissues [3,5]. In rice, increasing sucrose loading into the phloem through the expression of an Arabidopsis sucrose transporter (SUC2) has been reported to increase grain yield by 16% relative to control plants [6]. Sucrose degradation in the sink tissue will drive further sucrose import, and the levels of SUS and INV activity are a major determinant of sink strength [8,9,10]. In maize, increased SUS activity results in greater starch accumulation [11]

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Results

Discussion

Conclusion