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.

Preliminary investigation of phosphorus adsorption onto two types of iron oxide-organic matter complexes

Iron oxide（FeO）coated by natural organic matter（NOM）is ubiquitous.The associations of minerals with organic matter（OM）significantly changes their surface properties and reactivity,and thus affect the environmental fate of pollutants,including nutrients（e.g.,phosphorus（P））.In this study,ferrihydrite/goethite-humic acid（FH/GE–HA）complexes were prepared and their adsorption characteristics on P at various p H and ionic strength were investigated.The results indicated that the Fe O–OM complexes showed a decreased P adsorption capacity in comparison with bare Fe O.The maximum adsorption capacity（Q（max））decreased in the order of FH（22.17 mg/g）〉FH-HA（5.43 mg/g）〉GE（4.67 mg/g）〉GE-HA（3.27 mg/g）.After coating with HA,the amorphous FH–HA complex still showed higher P adsorption than the crystalline GE–HA complex.The decreased P adsorption observed might be attributed to changes of the Fe O surface charges caused by OM association.The dependence of P adsorption on the specific surface area of adsorbents suggests that the Fe O component in the complexes is still the main contributor for the adsorption surfaces.The P adsorptions on Fe O–HA complexes decreased with increasing initial p H or decreasing initial ionic strength.A strong dependence of P adsorption on ionic strength and p H may demonstrate that outer-sphere complexes between the OM component on the surface and P possibly coexist with inner-sphere surface complexes between the Fe O component and P.Therefore,previous over-emphasis on the contributions of original minerals to P immobilization possibly over-estimates the P loading capacity of soils,especially in humic-rich areas.