Gene flow at a fine scale is still poorly understood despite its recognized importance for plant population demographic and genetic processes. We tested the hypothesis that intensity of gene flow will be lower and strength of spatial genetic structure (SGS) will be higher in more peripheral populations because of lower population density. The study was performed on the predominantly selfing Avena sterilis and included: (1) direct measurement of dispersal in a controlled environment; and (2) analyses of SGS in three natural populations, sampled in linear transects at fixed increasing interplant distances. We found that in A.sterilis major seed dispersal is by gravity in close (less than 2m) vicinity of the mother plant, with a minor additional effect of wind. Analysis of SGS with six nuclear SSRs revealed a significant autocorrelation for the distance class of 1m only in the most peripheral desert population, while in the two core populations with Mediterranean conditions, no genetic structure was found. Our results support the hypothesis that intensity of SGS increases from the species core to periphery as a result of decreased withinpopulation gene flow related to low plant density. Our findings also show that predominant selfpollination and highly localized seed dispersal lead to SGS at a very fine scale, but only if plant density is not too high.

Twentythree species of Ulota from South and Central America have previously been reported. A revision of the species suggests that number should be reduced to thirteen (U.billbuckii, U.fuegiana, U.germana, U.larrainii, U.luteola, U.macrocalycina, U.macrodontia, U.magellanica, U.phyllantha, U.pusilla, U.pycnophylla, U.rhytiore and U.streptodon) with eight names (U.aurantiaca=U.pycnophylla, U.carinata=U.fuegiana, U.fernandeziana=U.fuegiana, U.glabella=U.fuegiana, U.lativentrosa=U.pusilla, U.lobbiana=U.germana, U.pygmaeothecia=U.luteola and U.rufula=U.germana) reduced to synonyms, as well as three varieties (U.fuegiana var. crispata=U.fuegiana, U.rufula var. fagicola=U.germana and U.rufula var. patagonica=U.fuegiana). The taxonomic status of two names (U.angustissima and U.ventricosa) remains ambiguous. The typification of five names (U.macrodontia, U.magellanica, U.nothofagi, U.persubulata and U.pygmaeothecia) is proposed here. With the first report of U.crispa for South America, the total number of species accepted here for this region is fourteen. Two species (i.e. U.phyllantha and U.crispa) occur in both Hemispheres, one species (i.e. U.rhytiore) is only present in the Northern Hemisphere, whereas the remaining eleven species are all restricted to the Southern Hemisphere. Among them, nine (U.billbuckii, U.fuegiana, U.larrainii, U.macrocalycina, U.macrodontia, U.magellanica, U.pusilla, U.pycnophylla and U.streptodon) are restricted to South America, and two (U.germana and U.luteola) are distributed in South America and Oceania. The peristomes and spores of seven accepted species are illustrated in SEM micrographs. A key to all accepted species as well as descriptions, illustrations, synonyms, ecological and geographic distributions, and discussions are provided.

Primula chungensis is a species with considerable floral and mating-system variation, including distylous (outcrossing), homostylous (selfing) and mixed populations that contain both outcrossing and selfing forms. We isolated 24 microsatellite markers from P.chungensis using Illumina MiSeq sequencing. Polymorphism and genetic diversity were then measured based on a sample of 24 individuals from a natural population in southern Tibet. All loci were polymorphic with the number of alleles per locus ranging from 2 to4. The observed and expected heterozygosity ranged from 0 to 1 and 0.219 to 0.708, respectively. The microsatellite markers we have identified will serve as valuable tools for the investigation of the population genetic structure and phylogeography of P.chungensis and will inform models of the evolutionary history of mating systems in the species.

Sulfur nutrition is crucial for plant growth and development, as well as crop yield and quality. Inorganic sulfate in the soil is the major sulfur source for plants. After uptake, sulfate is activated by ATP sulfurylase, and then gets assimilated into sulfurcontaining metabolites. However, the mechanism of regulation of sulfate levels by ATP sulfurylase is unclear. Here, we investigated the control of sulfate levels by miR395mediated regulation of APS1/3/4. Sulfate was overaccumulated in the shoots of miR395 overexpression plants in which the expression of the APS1, APS3, and APS4 genes was suppressed. Accordingly, reduced expression of miR395 caused a decline of sulfate concentration. In agreement with these results, overexpression of the APS1, APS3, and APS4 genes led to the reduction of sulfate levels. Differential expression of these three APS genes in response to sulfate starvation implied that they have different functions. Further investigation revealed that the regulation of sulfate levels mediated by miR395 depends on the repression of its APS targets. Unlike the APS1, APS3, and APS4 genes, which encode plastidlocalized ATP sulfurylases, the APS2 gene encodes a cytosolic version of ATP sulfurylase. Genetic analysis indicated that APS2 has no significant effect on sulfate levels. Our data suggest that miR395targeted APS genes are key regulators of sulfate concentration in leaves.

Stipa purpurea is widely distributed along a large precipitation gradient on the Tibetan Plateau. This implies that S.purpurea from different populations may have different responses to drought stress. To explore this we compared the morphological and physiological changes of S.purpurea seedlings cultivated from seeds from Gar County and Nagqu County after 7 and 14 days of drought stress and subsequent rewatering. The results showed that S.purpurea plants from the more arid Gar area were more tolerant to drought stress than that from Nagqu. To investigate the potential mechanisms underlying this difference, we used iTRAQ quantitative proteomics technology to analyze protein dynamics in S.purpurea samples treated with 7 days of drought stress and subsequent rewatering. The results indicated that, during the process of drought and rewatering treatments, there were differentially expressed proteins in either or both S.purpurea populations. These differential proteins were divided into 24 functional categories that were mainly associated with stress response, the antioxidant system, photosynthesis, carbohydrate metabolism, and posttranslational modifications. According to these results, we concluded that the molecular basis of stronger drought resistance likely lies in the specific upregulation or higher expression of many proteins involved in stress response, the antioxidant system, posttranslational modification and osmotic regulation in S.purpurea from Gar County compared with that from Nagqu. This study improves our understanding of the intraspecific differences in drought resistance within S.purpurea populations, which helps to understand the distribution of S.purpurea along the moisture gradient, as well as the effect of climate change on this species.

Jasmonate (JA), as an important signal, plays a key role in multiple processes of plant growth, deve
lopment and stress response. Nicotine and related pyridine alkaloids in tobacco (Nicotiana tabacum L.) are essential secondary metabolites. Whether environmental factors control nicotine biosynthesis and the underlying mechanism remains previously unreported. Here, we applied physiological and biochemical approaches to investigate how salt stress affects nicotine biosynthesis in tobacco. We found that salt stress induced the biosynthesis of JA, which subsequently triggered the activation of JAresponsive gene expression and, ultimately, nicotine synthesis. Bioinformatics analysis revealed the existence of many NtMYC2arecognized Gbox motifs in the promoter regions of NtLOX, NtAOS, NtAOC and NtOPR genes. Applying exogenous JA increased nicotine content, while suppressing JA biosynthesis reduced nicotine biosynthesis. Salt treatment could not efficiently induce nicotine biosynthesis in transgenic antiCOI1 tobacco plants. These results demonstrate that JA acts as the essential signal which triggers nicotine biosynthesis in tobacco after salt stress.