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Since 2011-2012, Maize lethal necrosis (MLN) has emerged in East Africa, causing massive yield loss and propelling research to identify viruses and virus populations present in maize. As expected, next generation sequencing (NGS) has revealed diverse and abundant viruses from the family Potyviridae, primarily sugarcane mosaic virus (SCMV), and maize chlorotic mottle virus (MCMV) (Tombusviridae), which are known to cause MLN by synergistic co-infection. In addition to these expected viruses, we identified a virus in the genus Polerovirus (family Luteoviridae) in 104/172 samples selected for MLN or other potential virus symptoms from Kenya, Uganda, Rwanda, and Tanzania. This polerovirus (MF974579) nucleotide sequence is 97% identical to maize-associated viruses recently reported in China, termed ‘maize yellow mosaic virus’ (MaYMV) and maize yellow dwarf virus (MaYMV; KU291101, KU291107, MYDV-RMV2; KT992824); and 99% identical to MaYMV (KY684356) infecting sugarcane and itch grass in Nigeria; 83% identical to a barley-associated polerovirus recently identified in Korea (BVG; KT962089); and 79% identical to the U.S. maize-infecting polerovirus maize yellow dwarf virus (MYDV-RMV; KT992824). Nucleotide sequences from ORF0 of 20 individual East African isolates collected from Kenya, Uganda, Rwanda, and Tanzania shared 98% or higher identity, and were detected in 104/172 (60.5%) of samples collected for virus-like symptoms, indicating extensive prevalence but limited diversity of this virus in East Africa. We refer to this virus as “MYDV-like polerovirus” until symptoms of the virus in maize are known. [ABSTRACT FROM AUTHOR]

Maize rough dwarf disease caused by Rice black-streaked dwarf virus (RBSDV) is the most important disease of maize in China. Although deploying disease resistant hybrids would be the most effective way to control the disease, development of resistant hybrids has been limited by virus transmission rates that are too low for effective screening. An efficient inoculation technique for RBSDV was developed using Laodelphax striatellus Fallen, in which a virus-free planthopper colony was developed and viruliferous planthoppers were obtained by allowing a 3- to 4-day acquisition access period on RBSDV-infected wheat plants. Planthoppers were then allowed a 25- to 28-day latent period on wheat seedlings followed by a 3-day inoculation access period on two-to-three-leaf stage maize seedlings. By 35 days postinoculation, susceptible hybrid 'Zhengdan 958', inbred lines of 'Ye 107' and 'Ye 478' plants showed 100% RBSDV infection with symptoms of stunting plants, darkening leaves and white waxy swellings on underside of leaves. At tasseling stage, average disease indices were from 96.4 to 100.0%. Enzyme-linked immunosorbent assays were correlated with the presence of symptoms. The high efficiency of RBSDV transmission obtained using this technique provides a reliable procedure to screen for RBSDV resistance in maize. [ABSTRACT FROM AUTHOR]

The effects of cytoplasmic protein synthesis and protein phosphatase activity on NADH:nitrate reductase (NR) activity, protein and transcript were examined in maize (Zea mays L.) seedling leaves. A rapid increase in NR activity, measured in the presence of 5 mM Mg2+, was found upon exposure of excised leaves to light. Inhibitors of protein phosphatase activity (okadaic acid [OKA] and microcystin [MC]-LR) completely prevented the increase in NR activity. The cytoplasmic protein synthesis inhibitor, cycloheximide (CHX). did not affect Mg2+ inhibition of NR activity during the dark-to-light transition. Vmax NR activity, measured in the presence of Pi and EDTA, remained constant or increased slightly in maize leaves during the first 2 h of the light period. OKA, MC-LR or CHX treatment caused a 40 to 50% reduction in Vmax NR activity during this time. Incorporation of 35S-Met into NR protein was reduced more than 90% by CHX and 80% by OKA. The inhibition of NR protein synthesis by CHX and OKA correlated with a 50 to 60% decrease in 35S-Met incorporation into total soluble protein over the treatment period. The increase in NR mRNA levels early in the light period was prevented by OKA and MC-LR, but not by CHX. OKA had a similar effect on sucrose phosphate synthase mRNA levels, but did not affect Catalase 1 or Catalase 3 mRNA accumulation. The data suggest that light-induced decreases in Mg2+ inhibition of NR activity and transcript levels are independent of new protein synthesis. The effects of OKA and MC-LR indicate that protein phosphatase activities could be involved, directly or indirectly, in the regulation of NR activity, protein synthesis and transcript accumulation. [ABSTRACT FROM AUTHOR]

Abstract: Mechanisms for genetic resistance to diseases caused by potyviruses, especially Maize dwarf mosaic virus (MDMV), in maize (Zea mays L.) remain unclear. Previous studies indicated that MDMV can replicate in and spread to groups of cells in maize leaves of the virus resistant inbred line Pa405, but systemic movement of the virus did not occur. In this study, the responses of Pa405 and the virus-susceptible inbred line Oh28 were compared in germinating maize embryos. Four days post inoculation (dpi), MDMV was detected immunocytochemically in 45% of resistant and 19% of susceptible shoots, respectively. Systemic movement of MDMV out of inoculated leaves occurred between 2 and 4 dpi in Oh28 seedlings. Microarray analysis was used to examine the effects of MDMV inoculation on gene expression in shoots of resistant and susceptible lines at 4 dpi. Approximately 15% of transcripts were differentially expressed between the resistant and susceptible lines. Of the transcripts with >10 fold greater expression in one line, more than 70% were up-regulated in the resistant line. Substantially fewer genes were differentially expressed in MDMV- and mock-inoculated shoots, with 21 and 30 genes being differentially regulated in the susceptible and resistant lines, respectively. For a subset of genes, differential expression was validated using quantitative real-time PCR. There was no clustering of differentially expressed transcripts in the previously identified QTLs important for MDMV resistance. These results provide a short list of virus responsive transcripts to begin to explain the resistance response in Pa405 versus the susceptible response in Oh28. [Copyright &y& Elsevier]