The genetic model plant Arabidopsis thaliana, like many plant species, experiences a range of edaphic conditions across its natural habitat. Such heterogeneity may drive local adaptation, though the molecular genetic basis remains elusive. Here, we describe a study in which we used genome-wide association mapping, genetic complementation, and gene expression studies to identify cis-regulatory expression level polymorphisms at the AtHKT1;1 locus, encoding a known sodium (Na+) transporter, as being a major factor controlling natural variation in leaf Na+ accumulation capacity across the global A. thaliana population. A weak allele of AtHKT1;1 that drives elevated leaf Na+ in this population has been previously linked to elevated salinity tolerance. Inspection of the geographical distribution of this allele revealed its significant enrichment in populations associated with the coast and saline soils in Europe. The fixation of this weak AtHKT1;1 allele in these populations is genetic evidence supporting local adaptation to these potentially saline impacted environments.

Flowering time (FT) is the developmental transition coupling an internal genetic program with external local and seasonal climate cues. The genetic loci sensitive to predictable environmental signals underlie local adaptation. We dissected natural variation in FT across a new global diversity set of 473 unique accessions, with >12,000 plants across two seasonal plantings in each of two simulated local climates, Spain and Sweden. Genome-wide association mapping was carried out with 213,497 SNPs. A total of 12 FT candidate quantitative trait loci (QTL) were fine-mapped in two independent studies, including 4 located within ±10 kb of previously cloned FT alleles and 8 novel loci. All QTL show sensitivity to planting season and/or simulated location in a multi-QTL mixed model. Alleles at four QTL were significantly correlated with latitude of origin, implying past selection for faster flowering in southern locations. Finally, maximum seed yield was observed at an optimal FT unique to each season and location, with four FT QTL directly controlling yield. Our results suggest that these major, environmentally sensitive FT QTL play an important role in spatial and temporal adaptation.genotype by environment interaction | pleiotropy | life history | efficient mixed-model association T iming of reproduction greatly affects fitness (including survival and fecundity) in many organisms, especially plants (1-3). It also has a major effect on yield in crop species (4, 5). Flowering time (FT) in the model plant Arabidopsis thaliana has been shown to be an important adaptive trait (1, 3, 6, 7). A. thaliana lives in a wide range of climates and habitats and shows variation in lifehistory timing across its native species range (6). When behaving as a winter annual, A. thaliana germinates in the fall, overwinters as a vegetative rosette, and flowers in spring or summer. The summer annual strategy begins with spring germination and summer flowering followed by extended seed dormancy, whereas a rapidcycling strategy can have multiple overlapping generations per year. This differentiation in life history is largely controlled by local seasonal cues but also is a genetic requirement for vernalization, which is heavily influenced by variation in major FT loci, FRIGIDA (FRI) (8) and FLOWERING LOCUS C (FLC) (9). A recent study has shown that environmental signals create critical windows of sensitivity to local climate and that genetic differences among accessions regulate life-history traits (10). Analysis of the sequences of different accessions suggests that molecular variation in FRI has been shaped by selection (11,12). FT in A. thaliana has been shown to exhibit a latitudinal cline, suggesting that natural selection has shaped FT along the continental range to local climatic/geographical conditions (13,14). Furthermore, an artificialselection experiment has shown that the natural allelic variation in FRI can predict the adaptive evolution in FT under spring conditions (7).The signaling pathways controlling FT in A. thaliana, includin...

severe aphid infestation . An additional threat posed by the aphid is its ability to transmit certain With an efficient greenhouse screening method, the first resistance plant viruses to soybean such as Alfalfa mosaic virus, Soyto the soybean aphid (Aphis glycines Matsumura) was found in cultivated soybean [Glycine max (L.) Merr.] germplasm. No resistance was bean dwarf virus, and Soybean mosaic virus (Sama et al., found in 1425 current North American soybean cultivars, 106 Maturity 1974; Iwaki et al., 1980; Hartman et al., 2001; Hill et al., Group (MG) 000 through VII Asian cultivars, and in a set of 11 'Clark' 2001; Clark and Perry, 2002). isolines possessing different pubescence traits. Dense pubescence did Aphis glycines and close relative A. gossypii, the cotton not provide protection against the soybean aphid. Resistance was or melon aphid, are the only aphid species found colonizdiscovered and established in three ancestors of North American ing soybean in the USA. In other parts of the world, A. genotypes: 'Dowling', 'Jackson', and PI 71506. Expression of resiscraccivora, Aulacorthum solani, and other species have tance in those genotypes was characterized in choice and nonchoice been found colonizing soybeans (D. Voegtlin, personal tests. In choice tests, significantly fewer aphids occurred on Dowling, communication, 2003). Jackson, and PI 71506 plants compared with susceptible cultivars (P ϭ Aphis glycines has a heteroecious, holocyclic life-cycle 0.05). Aphid populations did not develop on Dowling and Jackson in nonchoice tests, indicating that there was a negative impact on pattern (Guang-xue and Tie-sen, 1982). Rhamnus catharaphid fecundity on those cultivars. That evidence combined with ob-tica (buckthorn) is the primary host of A. glycines (Hartservations of aphid mortality on those cultivars suggested that antibioman et al., 2001) and soybean is a secondary host. In sis-type resistance contributed to the expression of resistance. Possible autumn, when the soybean crop matures, the aphid moves donors of resistance to Dowling and Jackson were identified. In nonto R. cathartica, where mating and oviposition occurs. The choice tests, population development on PI 71506 was not sigegg stage overwinters on R. cathartica. During the follownificantly different from development on susceptible cultivars, indicating spring, the eggs hatch and a few generations are proing that antixenosis was more important in that genotype. Resistance duced before alatae (winged females) fly to soybean. was expressed in all plant stages. Dowling provided season-long pro-Because A. glycines is a recent pest in the USA, a comtection against aphids equal to the use of the systemic insecticide imiprehensive integrated management approach to control dacloprid {1-[(6-Chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidini-mine} in a field test. Four other germplasm accessions, 'Sugao Zarai',

The soybean aphid (Aphis glycines Matsumura), a new pest of soybean [Glycine max (L.) Merr.], rapidly spread throughout North America after its arrival in 2000 and caused millions of dollars in economic losses. At present, the application of insecticides is the only means to control the soybean aphid. However, genetic resistance to the aphid was recently discovered in soybean germplasm and the soybean cultivar Dowling was identified as having strong antibiosis‐type aphid resistance. The objective of this study was to determine the inheritance of resistance to the soybean aphid in Dowling. Resistance in F1, F2, and F2–derived F3 (F2:3) families from crosses between Dowling and the two susceptible soybean cultivars Loda and Williams 82 was analyzed. All F1 plants were resistant to the aphid. Heterogeneity of segregation of F2 plants in 14 Dowling × Loda F2 families was nonsignificant (P = 0.16), and pooled F2 data, with 132 resistant to 45 susceptible plants, fit a 3:1 ratio (P = 0.90). F2 plants from Dowling × Williams 82 segregated 135 resistant to 44 susceptible, also fitting a 3:1 ratio (P = 0.89). Segregation among the F2:3 families fit a 1:2:1 monogenic inheritance pattern. These results indicated that a single dominant gene named Rag1 controlled resistance in Dowling. The monogenic dominant nature of resistance will enable breeders to rapidly convert existing susceptible cultivars to resistant cultivars using backcrossing procedures.

Although the final size of plant organs is influenced by environmental cues, it is generally accepted that the primary size determinants are intrinsic factors that regulate and coordinate cell proliferation and cell expansion. Here, we show that optimal proteasome function is required to maintain final shoot organ size in Arabidopsis (Arabidopsis thaliana). Loss of function of the subunit regulatory particle AAA ATPase (RPT2a) causes a weak defect in 26S proteasome activity and leads to an enlargement of leaves, stems, flowers, fruits, seeds, and embryos. These size increases are a result of increased cell expansion that compensates for a reduction in cell number. Increased ploidy levels were found in some but not all enlarged organs, indicating that the cell size increases are not caused by a higher nuclear DNA content. Partial loss of function of the regulatory particle non-ATPase (RPN) subunits RPN10 and RPN12a causes a stronger defect in proteasome function and also results in cell enlargement and decreased cell proliferation. However, the increased cell volumes in rpn10-1 and rpn12a-1 mutants translated into the enlargement of only some, but not all, shoot organs. Collectively, these data show that during Arabidopsis shoot development, the maintenance of optimal proteasome activity levels is important for balancing cell expansion with cell proliferation rates.The 26S proteasome (26SP) is a multisubunit, multicatalytic, 2.4-MD protease responsible for the degradation of proteins involved in various biological processes (Varshavsky, 2005;DeMartino and Gillette, 2007;Hanna and Finley, 2007;. Prior to their degradation, most 26SP target proteins are covalently modified with a polyubiquitin chain in a three-step enzymatic reaction . In addition to its central function in recognizing and degrading polyubiquitinated proteins, the 26SP can also degrade proteins that were not modified by polyubiquitination (Benaroudj et al., 2001;Lee et al., 2006;Pande et al., 2007).The 26SP consists of a cylindrical 20S core complex and two 19S regulatory particles that cap the 20S core on both ends. The 20S proteasome (20SP) is composed of seven related a-subunits and seven related b-subunits arranged in a stack of four heptameric rings. The outer rings are composed of a-subunits and the inner rings are composed of b-subunits, of which three have proteolytic activities described as caspase-, trypsin-, and chymotrypsin-like . The regulatory particles (RPs) serve as highly restrictive gatekeepers for the core protease. Each RP is composed of a lid subcomplex, which contains at least nine non-ATPase subunits designated RPN3, RPN5 to RPN9, RPN11, RPN12, and RPN15 and a base subcomplex that contains RPN1, RPN2, RPN13, and RPT1 to RPT6 subunits. The RPN10 and RPN13 subunits have been shown to recognize polyubiquitinated proteins; thus, they define the main interaction points of the 26SP with its target proteins (Young et al., 1998;Smalle and Vierstra, 2004;Husnjak et al., 2008;Schreiner et al., 2008). Ubiquitinated proteins can also int...