Identification of new cellular and molecular leaf growth regulators in maize (Zea mays) through characterization of mutants with impaired growth

Date: 14 October 2019

Venue: Campus Groenenborger, S.207 - Groenenborgerlaan 171 - 2020 Antwerpen (route: UAntwerpen, Campus Groenenborger)

Time: 2:00 PM

Organization / co-organization: Department of Biology

PhD candidate: Katrien Sprangers

Principal investigator: Gerrit Beemster

Short description: PhD defence Katrien Sprangers - Faculty of Science, Department of Biology


Understanding plant growth regulatory processes is a longstanding research topic. Different model systems have been used over the years to study growth. We use the maize (Zea mays) leaf growth zone to study growth. Its spatial developmental gradient of dividing and elongating cells, combined with its large size, enables the study of cell division and elongation within the same leaf at high spatial resolution. Since leaf growth is a three-dimensional process wherein three axes are involved, the ratio between growth in these axes defines the degree of anisotropic growth and finally leaf shape. We found that growth in the division zone is highly anisotropic and that the degree of anisotropy decreases in the elongation zone.

To reveal new molecular regulators of leaf growth, we used a forward genetic approach to characterize two newly isolated dwarf maize mutants; dil1-2 and dpl. The dil1-2 mutation was mapped to the DIL1 gene, encoding an AP2-type transcription factor. Besides its reduced growth phenotype, dil1-2 is also characterized by aberrant stomatal development, specifically affected in asymmetric divisions. The reduced growth is partially explained by stress and starvation, revealed by a transcriptome analysis, probably caused by reduced photosynthesis in response to the impaired stomatal functioning. Additionally, the transcriptome data and an interactome analysis revealed two potential direct growth inhibiting targets of DIL1, related to microtubule organization and auxin transport.

The dwarf & pale leaves (dpl) mutant is characterized by a pale leaf color which is caused by a reduction in chloroplast number and size, correlating with a reduced chlorophyll content. This has a negative effect on photosynthetic rates, which ultimately limits sugar availability, demonstrated by a severe drop in soluble and insoluble sugars. Exogenous sucrose application at the tip of the leaf restores growth rates of dpl to approximately wild type rates, proving that limited sugar availability can fully explain the growth phenotype of dpl. The dpl mutation could not be linked to a causal gene yet, but is located in an 11.58 Mb genomic region at the tail of chromosome 7.
Thus, by using the maize leaf growth zone model system to study growth inhibition in dwarf maize mutants, we have contributed to a more comprehensive understanding of leaf growth regulation. In addition, new cellular and molecular regulators that control stomatal development and chloroplast numbers were revealed.