No abstract

Communities of root-associated fungi (RAF) commonly have been studied under the auspices of arbuscular mycorrhizal fungi (AMF) or ectomycorrhizal fungi. However many studies now indicate that other groups of endophytic RAF, including dark septate endophytes (DSE) are more abundant in some plants and environments. The common forage grass, Bouteloua gracilis, was used as a model to examine whether RAF also colonize different organs within the same plant and to compare RAF communities from sites across North America, spanning the latitudinal range of B. gracilis (from Canada to Mexico). We compared the RAF communities of organs within individual plants at one site and within plant roots among six sites. With the possible exception of one group related to genus Paraphaeosphaeria there was little evidence that RAF colonized vertically beyond the crowns. Furthermore, although there was some variation in the constitution of rare members of the RAF communities, several taxonomically related groups dominated the RAF community at all sites. These dominant taxa included members in the Pleosporales (related to the DSE, Paraphaeosphaeria spp.), Agaricales (related to Moniliophthora spp., or Campanella spp.) and Hypocreales (related to Fusarium spp.). AMF were notable by their near absence. Similar phylotypes from the dominant groups clustered around adjacent sites so that similarity of the RAF communities was negatively correlated to site inter-distance and the RAF communities appeared to group by country. These results increase the possibility that at least some of these common and widely distributed core members of the RAF community form important, intimate and long lasting relationships with grasses.

The shoot apical meristem (SAM) maintains a pool of indeterminate cells within the SAM proper, while lateral organs are initiated from the SAM periphery. Laser microdissection–microarray technology was used to compare transcriptional profiles within these SAM domains to identify novel maize genes that function during leaf development. Nine hundred and sixty-two differentially expressed maize genes were detected; control genes known to be upregulated in the initiating leaf (P0/P1) or in the SAM proper verified the precision of the microdissections. Genes involved in cell division/growth, cell wall biosynthesis, chromatin remodeling, RNA binding, and translation are especially upregulated in initiating leaves, whereas genes functioning during protein fate and DNA repair are more abundant in the SAM proper. In situ hybridization analyses confirmed the expression patterns of six previously uncharacterized maize genes upregulated in the P0/P1. P0/P1-upregulated genes that were also shown to be downregulated in leaf-arrested shoots treated with an auxin transport inhibitor are especially implicated to function during early events in maize leaf initiation. Reverse genetic analyses of asceapen1 (asc1), a maize D4-cyclin gene upregulated in the P0/P1, revealed novel leaf phenotypes, less genetic redundancy, and expanded D4-CYCLIN function during maize shoot development as compared to Arabidopsis. These analyses generated a unique SAM domain-specific database that provides new insight into SAM function and a useful platform for reverse genetic analyses of shoot development in maize.

The importance of the warm‐season grass Paspalum vaginatum Sw. lies in its salt tolerance and its ability to serve as forage, ground cover for erosion control, and turf for sport surfaces in vulnerable areas in the tropics and subtropics. We conducted DNA content measurements using flow cytometry and diversity analyses using 43 simple sequence repeat (SSR) markers in a set of 97 Paspalum group Disticha accessions to resolve the relationship between the two group Disticha species, P. vaginatum Sw. and P. distichum L., and determine their ploidy level, genetic diversity, population structure, and distribution history. Using glume pubescence as a distinguishing characteristic, P. vaginatum accessions were largely diploid and P. distichum accessions largely polyploid, although exceptions were identified in both species. Transferability of genomic P. vaginatum SSRs to P. distichum confirmed the close genetic relationship between the two species. Similarity in SSR allele sizes between the two species may be an indication of gene flow. Population structure analyses grouped the germplasm into three subpopulations. One subpopulation consisted of accessions with mixed leaf texture, mixed glume pubescence phenotypes, and mixed ploidy levels. The other two subpopulations contained only diploid members with a typical P. vaginatum turf phenotype. Our data bring into question the distinguishing characteristics of P. distichum and P. vaginatum and whether they should be considered the same species. We also make some strategic recommendations for new collections and accession maintenance.