Salt stress (SS) has become an important factor limiting afforestation programs. Because of their salt tolerance and fully sequenced genomes, poplars (Populus spp.) are used as model species to study SS mechanisms in trees. Here, we review recent insights into the physiological and molecular responses of Populus to SS, including ion homeostasis and signaling pathways, such as the salt overly sensitive (SOS) and reactive oxygen species (ROS) pathways. We summarize the genes that can be targeted for the genetic improvement of salt tolerance and propose future research areas.

The complete chloroplast (cp) genome sequence of an endangered tree species, Zelkova schneideriana, was first assembled and characterized based on Illumina pair-end sequencing. The cp genome is 158,991 bp in length, with a quantitative structure comprising a pair of inverted repeats (IRs) of 26,427 bp separated by a large single copy (LSC) of 87,424 bp, a small single copy (SSC) of 18,713 bp. A total of 129 genes were annotated including 84 protein-coding genes, 37 tRNA genes, and 8 rRNA genes, respectively. Phylogenetic analysis based on the cp genomes indicates that Z. schneideriana is closely related to genus Ulums in Ulmaceae.

Alnus formosana (Betulaceae) is an important ecological and economic deciduous tree species widely distributed throughout subtropical regions of Taiwan province, China. At the present study, the complete chloroplast genome of A. formosana was assumbled using next-generation sequencing technology. The complete chloroplast sequence is 161,029 bp in length, which consisted of a large single copy (LSC, 89,720 bp) and a small single copy (SSC; 19,205 bp) separated a pair of inverted repeats (IRs; 26,052 bp). The overall guanine-cytosine (GC) content was 36.4%. A total of 131 genes were annotated, including 85 protein-coding genes, 37 tRNAs, eight rRNAs and one pseudogene (ψycf1). The phylogenetic analysis fully resolved A. formosana in a clade with A. japonica. The plastome of A. formosana will provide informative genomic resources for further phylogenetic application and genetic improvement.

Nanhaia speciosa (Fabaceae) is a woody perennial vine used as an important traditionally Chinese medicine. In this study, the complete chloroplast genome of Nanhaia speciosa was sequenced and assembled. The chloroplast genome of N. speciosa was 132,551bp in length including only one copy of the inverted repeat (IR). It encoded a total of 110 genes, containing 76 protein-coding genes, 30 tRNA and 4 rRNA. The overall GC content was 34.1%. Phylogenetic analysis using a matrix of 69 protein-coding genes illustrated that N. speciosa is most closely related to Wisteriopsis reticulata of tribe Wisterieae.