Tianhu Liang, Yu Hu, Na Xi, Minyan Zhang, Chaoying Zou, Fei Ge, Guangsheng Yuan, Shibin Gao, Suzhi Zhang, Guangtang Pan, Langlang Ma, Thomas Lübberstedt & Yaou Shen

Theoretical and Applied Genetics April 2023; vol. 136, Article number: 93

Published: April 3 2023

Figure: Explant (immature embryos) source (A), dissection and isolation of different sizes of explants (B & C), and their initial response on media supplemented with different concentrations of 2,4-D (D-F) in maize (Zea mays L.); immature embryos of 2 mm in size inoculated on the medium lacking hormones develop profuse roots and shoots without callus induction (D), immature embryos of <1 and >3 mm in size inoculated on the medium supplemented with 2,4-D seldom initiate callus formation (E & F).

(https://www.researchgate.net/publication/340478518_Distinctive_response_of_maize_Zea_mays_L_genotypes_in_vitro_with_the_acceleration_of_phytohormones/figures?lo=1 )

Key message

Combined GWAS, WGCNA, and gene-based association studies identified the co-expression network and hub genes for maize EC induction. ZmARF23 bound to ZmSAUR15 promoter and regulated its expression, affecting EC induction.

Abstract

Embryonic callus (EC) induction in immature maize embryos shows high genotype dependence, which limits the application of genetic transformation in transgenic breeding and gene function elucidation in maize. Herein, we conducted a genome-wide association mapping (GWAS) for four EC induction-related traits, namely rate of embryonic callus induction (REC), increased callus diameter (ICD), ratio of shoot formation (RSF), and length of shoot (LS) across different environments. A total of 77 SNPs were significantly associated these traits under three environments and using the averages (across environments). Among these significant SNPs, five were simultaneously detected under multiple environments and 11 had respective phenotypic variation explained > 10%. A total of 257 genes were located in the linkage disequilibrium decay of these REC- and ICD-associated SNPs, of which 178 were responsive to EC induction. According to the expression values of the 178 genes, we performed a weighted gene co-expression network analysis (WGCNA) and revealed an EC induction-associated module and five hub genes. Hub gene-based association studies uncovered that the intragenic variations in GRMZM2G105473 and ZmARF23 influenced EC induction efficiency among different maize lines. Dual-luciferase reporter assay indicated that ZmARF23 bound to the promoter of a known causal gene (ZmSAUR15) for EC induction and positively regulated its expression on the transcription level. Our study will deepen the understanding of genetic and molecular mechanisms underlying EC induction and contribute to the use of genetic transformation in maize.

See https://link.springer.com/article/10.1007/s00122-023-04341-x