The cytosolic isoform of triosephosphate isomerase,ZmTPI4,is required for kernel development and starch synthesis in maize(Zea mays L.)

Triosephosphate isomerase(TPI)is an enzyme that functions in plant energy production,accumulation,and conversion.To understand its function in maize,we characterized a maize TPI mutant,zmtpi4.In comparison to the wild type,zmtpi4 mutants showed altered ear development,reduced kernel weight and starch content,modified starch granule morphology,and altered amylose and amylopectin content.Protein,ATP,and pyruvate contents were reduced,indicating ZmTPI4 was involved in glycolysis.Although subcellular localization confirmed ZmTPI4 as a cytosolic rather than a plastid isoform of TPI,the zmtpi4 mutant showed reduced leaf size and chlorophyll content.Overexpression of ZmTPI4 in Arabidopsis led to enlarged leaves and increased seed weight,suggesting a positive regulatory role of ZmTPI4 in kernel weight and starch content.We conclude that ZmTPI4 functions in maize kernel development,starch synthesis,glycolysis,and photosynthesis.

An ARF24-ZmArf2 module influences kernel size in different maize haplotypes

Members of the ADP-ribosylation factor family,which are GTP-binding proteins, are involved in metabolite transport, cell division, and expansion.Although there has been a significant amount of research on small GTP-binding proteins, their roles and functions in regulating maize kernel size remain elusive. Here, we identified Zm Arf2 as a maize ADPribosylation factor-like family member that is highly conserved during evolution. Maize zmarf2 mutants showed a characteristic smaller kernel size. Conversely, ZmArf2 overexpression increased maize kernel size. Furthermore, heterologous expression of Zm Arf2 dramatically elevated Arabidopsis and yeast growth by promoting cell division. Using expression quantitative trait loci(e QTL) analysis, we determined that Zm Arf2 expression levels in various lines were mainly associated with variation at the gene locus. The promoters of Zm Arf2 genes could be divided into two types, p S and p L, that were significantly associated with both Zm Arf2 expression levels and kernel size. In yeast-one-hybrid screening, maize Auxin Response Factor 24(ARF24) is directly bound to the Zm Arf2 promoter region and negatively regulated Zm Arf2 expression.Notably, the p S and p L promoter types each contained an ARF24 binding element: an auxin response element(AuxRE) in p S and an auxin response region(Aux RR) in p L, respectively. ARF24binding affinity to Aux RR was much higher compared with Aux RE. Overall, our results establish that the small G-protein Zm Arf2 positively regulates maize kernel size and reveals the mechanism of its expression regulation.