Understanding Callus Types in Maize by Genetic Mapping and Transcriptional Profiling

Area of Science:

• Plant Biotechnology
• Maize Genetics
• Molecular Biology

Background:

• Plant transformation efficiency varies by species, genotype, and tissue.
• Immature maize embryos are key for transformation, relying on callus development for regeneration.
• Two main callus types, Type I and Type II, arise from maize immature embryos, with Type II being favorable for regeneration.

Purpose of the Study:

• To identify genetic factors controlling callus type determination in maize.
• To understand the genetic basis of Type II callus formation for improved transformation efficiency.
• To investigate gene expression differences between Type I and Type II calli and within heterogeneous A188 calli.

Main Methods:

• Genotyping-By-Sequencing (GBS) and Quantitative Trait Locus (QTL) analysis on a B73 x A188 F2 maize population.
• Bulk Segregant RNA-sequencing (BSR-seq) to analyze gene expression differences between callus types.
• Transcriptional comparison of fast- and slow-growing sectors within A188 calli.

Main Results:

• QTL analysis identified significant loci for callus type on maize chromosomes 2, 5, 6, 8, and 9.
• A188 alleles on chromosome 6 and B73 alleles on chromosomes 2, 5, 8, and 9 promote Type II callus formation.
• Differentially expressed genes (DEGs) between callus types and within heterogeneous calli were identified, enriched in cell-wall organization and wax biosynthesis pathways.

Conclusions:

• Genetic loci influencing maize callus type and regeneration potential have been mapped.
• Specific alleles from A188 and B73 parental lines contribute to desirable Type II callus formation.
• Gene expression analysis reveals pathways involved in callus growth and morphology, offering targets for improving maize transformation.