# Genetic and Phenotypic Characterization of a Novel dull1 Allele Affecting Starch Accumulation in Maize

## TL;DR

A new mutation in maize disrupts starch production, leading to changes in grain structure and composition, offering insights into improving crop quality.

## Contribution

Discovery of a novel loss-of-function allele, du1-2018, that affects starch accumulation and reveals transcriptional changes in nitrogen metabolism.

## Key findings

- The du1-2018 mutation causes reduced starch levels and altered starch granule structure in maize kernels.
- Transcriptomic analysis shows significant changes in genes related to amino acid and protein metabolism.
- The mutation is a severe loss-of-function allele of the dull1 gene with nearly undetectable Du1 transcripts.

## Abstract

Background: Starch accumulation contributes substantially to maize grain yield and quality. Starch synthase III (SSIII) is a key component of the starch biosynthetic enzyme complex. However, its regulatory role in starch accumulation in maize endosperm remains incompletely understood. Methods: The du1-2018 mutant arose spontaneously during a conventional maize breeding program. Phenotypic characterization, storage compound contents, and starch structure were compared between the mutant and wild-type lines. BSA-seq, genetic linkage analysis, and transcriptomic analysis were employed to identify the candidate gene responsible for the mutant phenotype. Transcriptome sequencing was performed on developing kernels to evaluate the genome-wide effects of the du1-2018 mutation. Results: The du1-2018 mutant exhibited dull, glassy, and mildly shrunken kernels, with decreased starch levels and elevated soluble sugar and protein contents. The du1-2018 mutation disrupted starch accumulation, resulting in smaller, irregularly shaped starch granules and significant changes in starch composition and fine structure. This mutation was identified as a severe loss-of-function allele of the dull1 (du1) gene, evidenced by almost undetectable Du1 transcripts in developing kernels. Notably, transcriptomic analysis revealed that a substantial proportion of differentially expressed genes (DEGs) were involved in amino acid and protein metabolism. Conclusions: The novel du1 allelic variant, du1-2018, disrupts starch biosynthesis in maize endosperm, leading to reduced starch accumulation, altered starch structure, and transcriptional changes in nitrogen-related metabolic pathways. Our results provide new insights into the regulatory mechanisms underlying SSIII function in starch synthesis and endosperm development, and suggest potential links to carbon/nitrogen balance, with implications for future genetic improvement of maize grain quality.