The chromosome-scale assembly of the willow genome provides insight into Salicaceae genome evolution

Salix suchowensis is an early-flowering shrub willow that provides a desirable system for studies on the basic biology of woody plants.The current reference genome of S.suchowensis was assembled with 454 sequencing reads.Here,we report a chromosome-scale assembly of S.suchowensis generated by combining PacBio sequencing with Hi-C technologies.The obtained genome assemblies covered a total length of 356 Mb.The contig N50 of these assemblies was 263,908 bp,which was~65-fold higher than that reported previously.The contiguity and completeness of the genome were significantly improved.By applying Hi-C data,339.67 Mb(95.29%)of the assembled sequences were allocated to the 19 chromosomes of haploid willow.With the chromosome-scale assembly,we revealed a series of major chromosomal fissions and fusions that explain the genome divergence between the sister genera of Salix and Populus.The more complete and accurate willow reference genome obtained in this study provides a fundamental resource for studying many genetic and genomic characteristics of woody plants.

Cloning and characterization of the PtVIP1 gene in Populus

The VirE2-interaction protein 1(VIP1)serves as a regulator of mitogen-activated protein kinase 3(MPK3)-mediated stress gene modulation under biotic stress,which in turn activates the MPK3 pathway in Arabidopsis.The mode of action of the VIP1 protein in Populus in response to biotic stress remains unknown.In this study,we cloned the full-length cDNA of the PtVIP1 gene from Populus trichocarpa(accession number of GenBank:KY793105).The VIP1 protein harboured a conserved bZIP(basic leucine zipper)domain located in the C-terminus.The VIP1 subcellular localization assay indicated that the VIP1 protein was present in the cytoplasm and nucleus under normal conditions,and that an increase in the amount of the protein in the nucleus occurred after treatment with flg22,the elicitor-active epitope of flagellin which triggers the innate immune response in plants.Transgenic Populus plants overexpressing VIP1 genes(PtVIP1 of Populus;or AtVIP1 of Arabidopsis,as positive control)were generated to investigate the role of VIP1 in vivo.The expression of poplar pathogenesis-related protein 1(PR1)genes was upregulated in transgenic-PtVIP1 or AtVIP1 poplar plants.The transgenic poplar plants overexpressing PtVIP1 or AtVIP1 also showed enhanced resistance to Brenneria salicis infection.These results suggest that the VIP1 protein accumulates in the nucleus in response to biotic stress,and that the pathogen resistance of transgenic VIP1 poplar may be associated with the induced expression of PR1 genes in response to pathogen challenge.

Natural infectious behavior of the urediniospores of Melampsora larici-populina on poplar leaves

The uredinial stage in the life cycle of Melampsora larici-populina on poplar leaves is the most important pathogenic phase. We captured partial phases of uredinial infection in the wild, aiming to reconstruct the process of uredinial ontogeny by using scanning and transmission electron microscope. At the initial infection stage, germ tubes germinated from the echinulate urediniospores. Germ tubes were frequently seen to merge with the leaf surface and cuticle breakage was observed, indicating direct hyphal penetration. Stomata penetration occurred commonly, sometimes with more than one germ tube penetrating the same stoma. Melampsora larici-populina did not form appressoria in the infection process,implying that infectious behavior of this pathogen may differ from the other rust pathogens. In general, germ tubes branched randomly, and no distinct evidence indicated that stoma could induce or orient germ tube branches. However, oriented germ tube growth has been occasionally observed in other studies. The urediniospores collapsed and finally wizened when they became nutrient stressed. At the last stage of infection, the uredinia erupted from the leaf epidermis and appeared as orange pustules on the leaf surface.

Reproductive Behaviors and Pairing Modes of Odontotermes fomosanus(Shiraki)Alates

[ Objectives ] To study the reproductive behaviors and the effect of different pairing modes on the developmental status of incipient colonies＇of Odontote- rmes fomosanus （Shiraki）. [ Methods ] We observed the reproductive behaviors of male alates, female Mates and mated alates respectively. Male and female Mates had 9 pairing modes and founded 170 incipient colonies under laboratory conditions. The effect of pairing mode on incipient colonies＇ developmental status was ana- lyzed. [ Results ] Two peaking hours of mating activity within the daily circadian rhythm of Mate activity appeared from 09：00 to 10：00, and from 21：00 to 22：00, respectively. Courtship behavior before mating consisted of touching with antennae, connecting into a ring （head-to-end）, and licking. The reproductive behavior （ calling, pairing, tandem, mating and oviposition） of nestmate pairs was different to that of non-nestmate pairs. The pairing time of non-nestmate pairs was signifi- candy longer than that of alates paired with siblings （P 〈 0.05 ）. The non-swarming alates could mate with swarming or non-swarming Mates and lay fertile eggs which hatched successfully. However, the survival rate of colonies founded by non-swarming alates was very low. The death rate of incipient colonies was in the range of 0.61% -0. 99% after three months, while the death rate of the colonies founded by swarming alates was in the range of 0.22% -0.58%. Females that had been experimentally prevented from mating could lay eggs, but the eggs did not hatch. [ Conclusion] There are two distinct hourly peaks of mating activity within each 24 hour period. Incipient colonies founded by outbreeding have the highest probability of survival.

Potential Impacts of Proposed Chenglingji Hydraulic Project on Wetlands in Dongting Lake

Water level fluctuation of is an important ecological character of lakes in monsoon climate zone.It is the key driver to seasonal change of the wetlands and associated habitats,which provide vital inhabiting conditions for different species in summer and winter,or,wet season and dry season.Due the hydrologic regime changes in the recent years after the operation of Three Gorges Dam,in 2012,the government of Hunan province proposed Chenglingji Hydraulic Project,aiming at water level control in dry season at Chenglingji,where the outlet of Dongting Lake located.Through different operations on water retreat process,five scenarios on the water level control from 21 m to 24 m were set in the plan.The potential ecological impacts of the project are under enormous public concern.To analyze potential impacts from different scenarios of water level control on the wetlands,this paper studied the topography of Dongting Lake bed and wetlands in dry season,by using Digital Elevation Model（DEM）and 15 images from HJ satellite and 1 image from Landsat TM.The wetlands at water levels of 19 m to 27 m were analyzed.The study revealed that there were 4 terrain steps on Dongting Lake bed from the West Dongting Lake to East Dongting Lake.Water level control at Chenglingji would increase area of open water in East Dongting Lake and Hengling Lake areas,while its effect on South Dongting Lake and West Dongting Lake areas due to higher terrain was weaker.Particularly,the area percentages of South Dongting Lake area did not change with water level fluctuation,due to its 2 elevation steps.The area percentages of various types of the wetlands in Dongting Lake area during the processes of water level rising and retreating were quite different,even in the relatively close water level interval.The retreating area of open water in autumn was larger than that during the spring flooding.The 23 m was the key water level,a turning point of the area change of the wetlands in Dongting Lake area.Areas of open water,mudflat,meadows and their percentages changed significantly at water levels above 23 meters,with increasing of open water area and shrinking of meadow area,their areas would decrease 30 000 ha.As the key habitats for wintering geese,the area of meadows was from near 70 000 ha to 10 000 ha.Among 5 scenarios,the impact of the scenario at 21 m elevation on wetlands was the weakest.However,water level dropping was still postponed than that of natural hydrological process in the scenarios.It resulted in longer inundation of large area of lakebed at elevation of 22-23 m,increasing habitats for aquatic biodiversity but reducing area of the meadows,where is the key habitat for wintering geese.All the other water level control scenarios would cause large area of inundation of lakebed in dry season and dramatic change of wetlands.To maintain the natural wetlands in Dongting Lake area,the Chenglingji Hydraulic Project should be considered in a more cautious way and further researches were needed on the response of aquatic biodiversity and wintering water birds.

Synthetic promoters consisting of defined cis-acting elements link multiple signaling pathways to probenazole-inducible system

Probenazole （3-allyloxy-l,2-benzisothiazole-1,1-dioxide, PBZ）, the active component of Oryzemate, could induce systemic acquired resistance （SAR） in plants through the induction of salicylic acid （SA） biosynthesis. As a widely used chemical inducer, PBZ is a good prospect for establishing a new chemical-inducible system. We first designed artificially synthetic promoters with tandem copies of a single type of cis-element （SARE, JERE, GCC, GST1, HSRE, and W-box） that could mediate the expression of the tS-glucuronidase （GUS） reporter gene in plants upon PBZ treatment. Then we combined different types of elements in order to improve inducibility in the PBZ-inducible system. On the other hand, we were surprised to find that the cis-elements, which are responsive to jasmonic acid （JA） and ethylene, also responded to PBZ, implying that SA, JA, and ethylene pathways also would play important roles in PBZ＇s action. Further analysis demonstrated that PBZ also induced early events of innate immunity via a signaling pathway in which Ca2＋ influx and mitogen-activated protein kinase （MAPK） activity were involved. We constructed synthesized artificial promoters to establish a PBZ chemical-inducible system, and preliminarily explored SA, JA, ethylene, calcium, and MAPK signaling pathways via PBZ-inducible system, which could provide an insight for in-depth study.