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Acta Agronomica Sinica ›› 2025, Vol. 51 ›› Issue (6): 1569-1581.doi: 10.3724/SP.J.1006.2025.43056

• TILLAGE & CULTIVATION · PHYSIOLOGY & BIOCHEMISTRY • Previous Articles     Next Articles

Genetic analysis and molecular identification of a small kernel mutant mn-like1 in maize

YUAN Xin1,ZHAO Zhuo-Fan2,ZHAO Rui-Qing1,LIU Xiao-Wei1,ZHENG Ming-Min3,LIU Yu-Sheng4,DONG Hao-Sheng4,DENG Li-Juan4,CAO Mo-Ju1,*,HUANG Qiang4,*   

  1. 1 Maize Research Institute, Sichuan Agricultural University / Key Laboratory of Biology and Genetic of Maize in Southwest Region, Ministry of Agriculture and Rural Affairs,Chengdu 611130, Sichuan, China; 2 Chengdu University of Technology, Chengdu 610051, Sichuan, China; 3 College of Chemistry and Life Sciences, Chengdu Normal University, Chengdu 611130, Sichuan, China; 4 Sichuan Institute of Atomic Energy / Irradiation Preservation and Effect Key Laboratory of Sichuan Province, Chengdu 610101, Sichuan, China
  • Received:2024-12-10 Revised:2025-03-26 Accepted:2025-03-26 Online:2025-06-12 Published:2025-04-08
  • Supported by:
    This study was supported by Sichuan Science and Technology Program (2022NSFSC0018, 2021YFYZ0011, 2024NSFSC1210, 2023YFH0020).

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Abstract:

The kernel serves as the primary storage organ in maize, and its proper development requires on an adequate carbohydrate supply and efficient nutrient transport channels. In this study, we identified a natural mutant, small kernel 18 (smk18), exhibiting defects in kernel development. After multi-year and multi-location field trials, the smk18 mutant trait remained genetically stable. Segregation analysis of the (B73 × smk18) F2 population revealed that the mutant phenotype was controlled by a single recessive gene. The smk18 mutant was backcrossed to the inbred line RP125 for five generations to construct the near-isogenic mn-like1 (RP125smk18 smk18). Phenotypic evaluation showed that mn-like1 exhibited increased plant height and ear height compared to RP125, whereas hundred-kernel weight, kernel length, and kernel width were significantly reduced. Through molecular mapping, we localized the causal gene between Indel 4 and Indel 5 on chromosome 2. Within this interval, the Miniature1 (Mn1) gene had been previously reported to encode a cell wall invertase (INCW2) essential for carbohydrate transport during early kernel development. Sequencing of the Mn1 coding sequence (CDS) in mn-like1 revealed a 9-bp deletion in exon 5, leading to the loss of three amino acids (positions 409–411) in the Mn1 protein and alterations in its structure. Expression analysis showed that Mn1 transcript levels were significantly reduced in mn-like1 kernels at 13 days after pollination (DAP). An allelism test between mn-like1 and the transposon insertion mutant mn1-mu confirmed that mn-like1 is a novel allelic variant of Mn1. Further subcellular localization studies, carbohydrate quantification, and glycogen staining indicated that Mn1 is specifically expressed in the basal transfer layer of the endosperm. Mutation of Mn1 disrupted carbohydrate transport, leading to a significant reduction in sucrose and starch content in mn-like1 kernels, ultimately resulting in kernel developmental defects. In conclusion, this study expands the repertoire of Mn1 mutants in diverse genetic backgrounds and provides valuable genetic resources for elucidating the regulatory mechanisms of Mn1 in kernel development and the catalytic function of Mn1 protein.

Key words: maize, gene mapping, nutrient transport, cell wall invertase, kernel development

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