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Recent reverse genetics technologies have enabled genetic manipulation of plant negative‐strand RNA virus (NSR) genomes. Here, we report construction of an infectious clone for the maize‐infecting Alphanucleorhabdovirus maydis, the first efficient NSR vector for maize. The full‐length infectious clone was established using agrobacterium‐mediated delivery of full‐length maize mosaic virus (MMV) antigenomic RNA and the viral core proteins (nucleoprotein N, phosphoprotein P, and RNA‐directed RNA polymerase L) required for viral transcription and replication into Nicotiana benthamiana. Insertion of intron 2 ST‐LS1 into the viral L gene increased stability of the infectious clone in Escherichia coli and Agrobacterium tumefaciens. To monitor virus infection in vivo, a green fluorescent protein (GFP) gene was inserted in between the N and P gene junctions to generate recombinant MMV‐GFP. Complementary DNA (cDNA) clones of MMV‐wild type (WT) and MMV‐GFP replicated in single cells of agroinfiltrated N. benthamiana. Uniform systemic infection and high GFP expression were observed in maize inoculated with extracts of the infiltrated N. benthamiana leaves. Insect vectors supported virus infection when inoculated via feeding on infected maize or microinjection. Both MMV‐WT and MMV‐GFP were efficiently transmitted to maize by planthopper vectors. The GFP reporter gene was stable in the virus genome and expression remained high over three cycles of transmission in plants and insects. The MMV infectious clone will be a versatile tool for expression of proteins of interest in maize and cross‐kingdom studies of virus replication in plant and insect hosts. [ABSTRACT FROM AUTHOR]

Invasive annual cheatgrass (Bromus tectorum L.) and medusahead wildrye [ Taeniatherum caputmedusae (L.) Nevski ssp. asperum (Simonk.) Melderis] have decreased livestock productivity and biological diversity and increased the frequency of wildfire on rangelands in the western United States. On disturbed sites, squirreltail (Elymus sp.), a short-lived North American perennial, appears to compete against invasive exotic annuals when available soil N and nitrification are reduced. We tested the hypothesis that differences in N uptake activity could account for this phenomenon. North American seedlings of perennial bluebunch wheatgrass [Pseudoraegneria spicata (Pursh) A. Love], four populations of squirreltail, and two invasive exotic annuals were cultured in the laboratory on N[H.sub.4.sup.+], N[O.sub.3.sup.-], or N[H.sub.4]N[O.sub.3] nutrient solutions, and N uptake activity (mol [kg.sup.-1] root dry wt. [h.sup.-1]) was measured. The overall biomass means of 4-wk-old seedlings cultured with N[O.sub.3.sup.-], N[H.sub.4]N[O.sub.3], and N[H.sub.4.sup.+] were 72, 67, and 42 mg [seedling.sup.-1], respectively. Regardless of N form, cheatgrass biomass was as much as 4.2-fold greater than any of the other grasses including medusa head, which exceeded the biomass of all perennials except one. Cheatgrass had 1.5- to 2.2-fold greater N[O.sub.3.sup.-] uptake activity than the perennials, but the N[O.sub.3.sup.-] uptake activity of medusa head exceeded only two of the squirreltail populations. Ammonium uptake activities of perennials were not consistently more favorable than those of the annuals. The vigorous seedling growth of the invasive annuals coupled with the greater N[O.sub.3.sup.-] uptake activity of cheatgrass appear to be primary traits of the invasive annuals, driving their superior N capture and competition compared with these North American perennial grasses. Abbreviations: DAP, days after planting. doi: 10.2136/sssaj2008.0334

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]