In triploid watermelon (Citrullus lanatus), the homologous chromosomes of germ cells are disorder during meiosis, resulting in the failure of seeds formation and producing seedless fruit. Therefore, mutating the genes specifically functioning in meiosis may be an alternative way to achieve seedless watermelon. REC8, as a key component of the cohesin complex in meiosis, is dramatically essential for sister chromatid cohesion and chromosome segregation. However, the role of REC8 in meiosis has not yet been characterized in watermelon. Here, we identified ClREC8 as a member of RAD21/REC8 family with a high expression in male and female flowers of watermelon. In situ hybridization analysis showed that ClREC8 was highly expressed at the early stage of meiosis during pollen formation. Knocking out ClREC8 in watermelon led to decline of pollen vitality. After pollinating with foreign normal pollen, the ovaries of ClREC8 knockout lines could inflate normally but failed to form seeds. We further compared the meiosis chromosomes of pollen mother cells in different stages between the knockout lines and the corresponding wild type. The results indicated that ClREC8 was required for the monopolar orientation of the sister kinetochores in Meiosis I. Additionally, transcriptome sequencing (RNA-seq) analysis between WT and the knockout lines revealed that the disruption of ClREC8 caused the expression levels of mitosis-related genes and meiosis-related genes to decrease. Our results demonstrated ClREC8 has a specific role in Meiosis I of watermelon germ cells, and loss-of-function of the ClREC8 led to seedless fruit, which may provide an alternative strategy to breed cultivars with seedless watermelon.

Betula nana L. is a deciduous shrub belonging to the Betulaceae family, which is recorded as endangered species in the Red List. The complete chloroplast genome of B. nana was reported in this study. The size of the B. nana chloroplast genome is 160,579 bp, with an average GC content of 36.1 %. This circular molecule has a typical quadripartite structure containing a large single copy region of 89,492 bp, a small single copy region of 19,343 bp, and two inverted repeat regions of 25,872 bp. It encodes an identical set of 114 unique genes, including 79 protein coding, 31 transfer RNA and 4 ribosomal RNA genes. The total of 20 genes were duplicated in the inverted repeats. A maximum likelihood phylogenetic tree supported that the chloroplast genome of B. nana is closely related to that of Ostrya rehderiana.

Carya sinensis (Chinese Hickory, beaked walnut, or beaked hickory) is an endangered species that needs urgent conservation action. Here, we reported the complete chloroplast (cp) genome sequence and the genomic features of the C. sinensis cp, which is the first complete cp genome of any member of Carya . The C. sinensis cp genome was 160,195 bp, containing a large single copy region (LSC) of 89,541 bp and a small single copy region (SSC) of 18,538 bp separated by a pair of 26,058 bp inverted repeat regions (IRs). The genome contained 135 genes, including 87 protein-coding genes (79 species), 40tRNA genes (30tRNA species) and eight ribosomal RNA genes (four rRNA species). Most genes occurred as a single copy; 22 were duplicated. The overall GC content of the C. sinensis cp genome was 36.3 %; the corresponding GC content values of the LSC, SSC and IR regions were 33.9, 30.0 and 42.5 %, respectively. A maximum likelihood (ML) phylogenetic analysis showed that C. sinensis is closely related to Juglans , as expected based on taxonomic affinity. The complete cp genome of C. sinensis will be useful for further investigations of genetic diversity and conservation of this endemic relict woody plant.

The Chinese walnut (Juglans cathayensis L.), valued for both its nut and wood, is an ecologically important tree species endemic temperate southern China. Investigation of the genetic diversity of Chinese walnut has been limited to natural population genetics and genetic germplasm resources. Here, we describe the development of 12 polymorphic microsatellite markers using next-generation sequencing to screen 96 Chinese walnut individuals collected from 11 natural populations. The number of alleles per locus ranged from 5 to 12. The observed heterozygosity (0.288-0.748) overlapped well with the expected heterozygosity (0.337-0.751). This species has high genetic diversity and gene flow among different populations (F-ST = 0.075, Nm = 3.088). These markers will be useful for future studies on population genetic structure, evolutionary ecology, and genetic breeding of this walnut tree or other Juglans species. (C) 2015 Elsevier Ltd. All rights reserved.

Oxytropis ochrocephala Bunge is a poisonous legume plant which exhibits drought acclimation behavior and spreads rapidly under adverse environment. This study demonstrates that the stress signals including NO (nitric oxide), ABA (abscisic acid), and H2O2 (Hydrogen peroxide) are involved in roots of O. ochrocephala seedlings when exposed to drought stress simulated by PEG-6000 solution. The relationship among these signals was investigated by using exogenous and endogenous modulators. The results indicate that a time course of NO is accumulated in roots of O. ochrocephala in response to drought stress, which is generated enzymatically by nitrate reductase (NR) activity. The low level of NO acts as a downstream signaling of ABA and is involved with H2O2 signaling cascade. There is a regulatory mechanism of controlling NO concentration and maintaining the equilibrium state between ROS (reactive oxygen species) and NO, which modulates the root cell vitality, and osmotic adjustment thus improves root growth and developmental processes under drought stress.