Search

Summary: Nuclear‐cytoplasmic trafficking is crucial for protein synthesis in eukaryotic cells due to the spatial separation of transcription and translation by the nuclear envelope. However, the mechanism underlying this process remains largely unknown in plants.In this study, we isolated a maize (Zea mays) mutant designated developmentally delayed kernel 1 (ddk1), which exhibits delayed seed development and slower filling. Ddk1 encodes a plant‐specific protein known as Importin‐4 β, and its mutation results in reduced 80S monosomes and suppressed protein synthesis.Through our investigations, we found that DDK1 interacts with eIF1A proteins in vivo. However, in vitro experiments revealed that this interaction exhibits low affinity in the absence of RanGTP. Additionally, while the eIF1A protein primarily localizes to the cytoplasm in the wild‐type, it remains significantly retained within the nuclei of ddk1 mutants. These observations suggest that DDK1 functions as an exportin and collaborates with RanGTP to facilitate the nuclear export of eIF1A, consequently regulating endosperm development at the translational level.Importantly, both DDK1 and eIF1A are conserved among various plant species, implying the preservation of this regulatory module across diverse plants. [ABSTRACT FROM AUTHOR]

Maize kernels are complex biological systems composed of three genetic sources, namely maternal tissues, progeny embryos, and progeny endosperms. The lack of gene expression profiles with spatial information has limited the understanding of the specific functions of each cell population, and hindered the exploration of superior genes in kernels. In our study, we conduct microscopic sectioning and spatial transcriptomics analysis during the grain filling stage of maize kernels. This enables us to visualize the expression patterns of all genes through electronical RNA in situ hybridization, and identify 11 cell populations and 332 molecular marker genes. Furthermore, we systematically elucidate the spatial storage mechanisms of the three major substances in maize kernels: starch, protein, and oil. These findings provide valuable insights into the functional genes that control agronomic traits in maize kernels. Maize kernels have long intrigued researchers due to their complex structure. Through microscopic sectioning and spatial transcriptomics, the authors observed the spatial distribution of RNA through electronic RNA in situ hybridization maps and discovered how storage accumulation occurs. [ABSTRACT FROM AUTHOR]

Mutation of o2 doubles maize endosperm lysine content, but it causes an inferior kernel phenotype. Developing quality protein maize (QPM) by introgressing o2 modifiers (Mo2s) into the o2 mutant benefits millions of people in developing countries where maize is a primary protein source. Here, we report genome sequence and annotation of a South African QPM line K0326Y, which is assembled from single-molecule, real-time shotgun sequencing reads collinear with an optical map. We achieve a N50 contig length of 7.7 million bases (Mb) directly from long-read assembly, compared to those of 1.04 Mb for B73 and 1.48 Mb for Mo17. To characterize Mo2s, we map QTLs to chromosomes 1, 6, 7, and 9 using an F2 population derived from crossing K0326Y and W64Ao2. RNA-seq analysis of QPM and o2 endosperms reveals a group of differentially expressed genes that coincide with Mo2 QTLs, suggesting a potential role in vitreous endosperm formation. The South African quality protein maize (QPM) cultivars have the desired high lysine content and kernel hardness due to o2 mutation and the introgression of modifiers of o2 (Mo2) QTLs, respectively. Here, the authors assemble the genome of a QPM line and identify candidate genes underlying Mo2 QTLs. [ABSTRACT FROM AUTHOR]

The mechanism that creates vitreous endosperm in the mature maize kernel is poorly understood. We identified Vitreous endosperm 1 (Ven1) as a major QTL influencing this process. Ven1 encodes β-carotene hydroxylase 3, an enzyme that modulates carotenoid composition in the amyloplast envelope. The A619 inbred contains a nonfunctional Ven1 allele, leading to a decrease in polar and an increase in non-polar carotenoids in the amyloplast. Coincidently, the stability of amyloplast membranes is increased during kernel desiccation. The lipid composition in endosperm cells in A619 is altered, giving rise to a persistent amyloplast envelope. These changes impede the gathering of protein bodies and prevent them from interacting with starch grains, creating air spaces that cause an opaque kernel phenotype. Genetic modifiers were identified that alter the effect of Ven1A619, while maintaining a high β-carotene level. These studies provide insight for breeding vitreous kernel varieties and high vitamin A content in maize. Very little is known about how vitreous endosperm in the mature maize kernel is created. Here, via map-based cloning, the authors find that mutation of a β-carotene hydroxylase 3 encoding gene Ven1 affects carotenoids and lipids composition, which consequently influences amyloplast envelope integrity. [ABSTRACT FROM AUTHOR]

The organic acid oxalate occurs in microbes, animals, and plants; however, excessive oxalate accumulation in vivo is toxic to cell growth and decreases the nutritional quality of certain vegetables. However, the enzymes and functions required for oxalate degradation in plants remain largely unknown. Here, we report the cloning of a maize (Zea mays) opaque endosperm mutant that encodes oxalyl-CoA decarboxylase1 (EC4.1.1.8; OCD1). Ocd1 is generally expressed and is specifically induced by oxalate. The ocd1 mutant seeds contain a significantly higher level of oxalate than the wild type, indicating that the ocd1 mutants have a defect in oxalate catabolism. The maize classic mutant opaque7 (o7) was initially cloned for its high lysine trait, although the gene function was not understood until its homolog in Arabidopsis thaliana was found to encode an oxalyl-CoA synthetase (EC 6.2.1.8), which ligates oxalate and CoA to form oxalyl-CoA. Our enzymatic analysis showed that ZmOCD1 catalyzes oxalyl-CoA, the product of O7, into formyl-CoA and CO2 for degradation. Mutations in ocd1 caused dramatic alterations in the metabolome in the endosperm. Our findings demonstrate that ZmOCD1 acts downstream of O7 in oxalate degradation and affects endosperm development, the metabolome, and nutritional quality in maize seeds. [ABSTRACT FROM AUTHOR]