Functional analysis of ZmG6PE reveals its role in responses to low-phosphorus stress and regulation of grain yield in maize.

A previous metabolomic and genome-wide association analysis of maize screened a glucose-6-phosphate 1-epimerase (ZmG6PE) gene, which responds to low-phosphorus (LP) stress and regulates yield in maize's recombinant inbred lines (RILs). However, the relationship of ZmG6PE with phosphorus and yield remained elusive. This study aimed to elucidate the underlying response mechanism of the ZmG6PE gene to LP stress and its consequential impact on maize yield. The analysis indicated that ZmG6PE required the Aldose_epim conserved domain to maintain enzyme activity and localized in the nucleus and cell membrane. The zmg6pe mutants showed decreased biomass and sugar contents but had increased starch content in leaves under LP stress conditions. Combined transcriptome and metabolome analysis showed that LP stress activated plant immune regulation in response to the LP stress through carbon metabolism, amino acid metabolism, and fatty acid metabolism. Notably, LP stress significantly reduced the synthesis of glucose-1-phosphate, mannose-6-phosphate, and ß-alanine-related metabolites and changed the expression of related genes. ZmG6PE regulates LP stress by mediating the expression of ZmSPX6 and ZmPHT1.13. Overall, this study revealed that ZmG6PE affected the number of grains per ear, ear thickness, and ear weight under LP stress, indicating that ZmG6PE participates in the phosphate signaling pathway and affects maize yield-related traits through balancing carbohydrates homeostasis.

Identification of a new mutant allele of ZmYSL2 that regulates kernel development and nutritional quality in maize.

The discovery and characterization of the opaque endosperm gene provide ideas and resources for the production and application of maize. We found an o213 mutant whose phenotype was opaque and shrunken endosperm with semi-dwarf plant height. The protein, lipid, and starch contents in the o213 endosperm were significantly decreased, while the free amino acid content in the o213 endosperm significantly increased. The aspartic acid, asparagine, and lysine contents were raised in the o213 endosperm by 6.5-, 8.5-, and 1.7-fold, respectively. Genetic analysis showed that this o213 mutant is a recessive single-gene mutation. The position mapping indicated that o213 is located in a 468-kb region that contains 11 protein-encoding genes on the long arm of chromosome 5. The coding sequence analysis of candidate genes between the WT and o213 showed that ZmYSL2 had only a single-base substitution (A-G) in the fifth exon, which caused methionine substitution to valine. Sequence analysis and the allelic test showed that o213 is a new mutant allele of ZmYSL2. The qRT-PCR results indicated that o213 is highly expressed in the stalks and anthers. Subcellular localization studies showed that o213 is a membrane transporter. In the variation analysis of o213, the amplification of 65 inbred lines in GWAS showed that this 3-bp deletion of the first exon of o213 was found only in temperate inbred lines, implying that the gene was artificially affected in the selection process. Our results suggest that o213 is an important endosperm development gene and may serve as a genetic resource. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-022-01278-9.

Identification, Association of Natural Variation and Expression Analysis of ZmNAC9 Gene Response to Low Phosphorus in Maize Seedling Stage.

Phosphorus (P) is an essential macroelement supporting maize productivity and low-P stress is a limiting factor of maize growth and yield. Improving maize plant tolerance to low P through molecular breeding is an effective alternative to increase crop productivity. In this study, a total of 111 diverse maize inbred lines were used to identify the favorable alleles and nucleotide diversity of candidate ZmNAC9, which plays an important role in response to low P and regulation in root architecture. A significant difference was found under low- and sufficient-P conditions for each of the 22 seedling traits, and a total of 41 polymorphic sites including 32 single nucleotide polymorphisms (SNPs) and 9 insertion and deletions (InDels) were detected in ZmNAC9 among 111 inbred lines. Among the 41 polymorphic studied sites, a total of 39 polymorphic sites were associated with 20 traits except for the dry weight of shoots and forks, of which six sites were highly significantly associated with a diverse number of low-P tolerant root trait index values by using a mixed linear model (MLM) at -log10 P = 3.61. In addition, 29 polymorphic sites under P-sufficient and 32 polymorphic sites under P-deficient conditions were significantly associated with a diverse number of seedling traits, of which five polymorphic sites (position S327, S513, S514, S520, and S827) were strongly significantly associated with multiple seedling traits under low-P and normal-P conditions. Among highly significant sites, most of the sites were associated with root traits under low-P, normal-P, and low-P trait index values. Linkage disequilibrium (LD) was strong at (r2 > 1.0) in 111 inbred lines. Furthermore, the effect of five significant sites was verified for haplotypes in 111 lines and the favorable allele S520 showed a positive effect on the dry weight of roots under the low-P condition. Furthermore, the expression pattern confirmed that ZmNAC9 was highly induced by low P in the roots of the P-tolerant 178 inbred line. Moreover, the subcellular localization of ZmNAC9 encoded by protein was located in the cytoplasm and nucleus. Haplotypes carrying more favorable alleles exhibited superior effects on phenotypic variation and could be helpful in developing molecular markers in maize molecular breeding programs. Taken together, the finding of this study might lead to further functions of ZmNAC9 and genes that might be involved in responses to low-P stress in maize.