Maize, from crop to model plant

29 September 2015
​Mechanisms that determine the size of plants have fascinated plant scientists of all times. Although they are far from understood, insight into this is progressing and points towards dynamic protein-protein interactions that define the interplay between cell division and cell expansion. Dissecting molecular interactions with high resolution precision relies on detailed sampling. Therefore Geert De Jaeger’s group together with Hilde Nelissen and Dirk Inzé (VIB Department of Plant Systems Biology, UGent), Kris Gevaert (VIB Medical Biotechnology Center, UGent) and colleagues at the Iowa State University (US) have used the maize leaf to identify changes in protein complex composition in a growing organ. By means of tandem affinity purification, different sets of interacting proteins have been identified throughout the growing leaf and the functionality of these interactions has been determined.

Year after year, the TAP-tagging technique confirms its power for identifying new protein-protein interactions. Can you explain what makes this step to use maize so innovative?
Geert: This paper is not merely about introducing tandem affinity purification in a crop with high agronomical importance such as maize, but it also changes the way we think about organ growth. The processes of cell division and cell expansion occur spatially separated along the maize leaf and
its size allows for enriched sampling of dividing and expanding cells that is sufficient for proteomic
analyses. This study elegantly shows that changes in protein-protein interactions regulate developmental decisions, such as the transition from cell division to cell expansion. To our knowledge, this is the first time that changes in protein complex composition have been identified in a growing plant organ. The study identified multiple GROWTH-REGULATING FACTORS that function through the chromatin remodeling complex.

Can you explain how it works?
Hilde: DNA is packed in a condensed structure called chromatin. When certain genes need to be activated, the chromatin is unpacked to make specific DNA regions accessible. This process is mediated by socalled “chromatin remodeling” complexes. Depending on growth process, different members of the GROWTHREGULATING FACTOR (GRF) family have been found to be associated with such a chromatin remodeling complex to facilitate transcription of specific target genes: some GRFs were found to be specific for the division zone, while other GRFs were present in both dividing and
expanding cells. Functional analysis of the GRFs showed that the transition from cell division to cell expansion depends on the balance between these GRFs.

In this study, maize is used as a model organism, rather than as a tool for translational research?
Dirk: Indeed, for some biological questions, maize is an excellent plant model. For instance, this study would not have been possible in Arabidopsis because the size of its growing leaves is too small to reach the desired sampling resolution. However, we also continue to use maize to test our findings from Arabidopsis research and examine how relevant our greenhouse observations are for agronomical traits in the field.

Nelissen et al., Plant Cell 2015

After starting its second GM maize field trial at the ILVO site in Wetteren at the end of April, the VIB Plant Systems Department also started their own field trials with non-GM maize on a small site on the Technologiepark in Zwijnaarde. Different inbred and hybrid lines are grown and characterized to support the research work of the units of Dirk Inzé (yield), Moritz Novak (programmed cell death) and Steven Maere (evolutionary systems biology). The GM maize that is grown in Wetteren has been modified to express an additional factor involved in the regulation of plant organ growth.

Dirk Inzé, Hilde Nelissen and Geert De Jaeger
@VIB, 2015