In 2003, Kandelia obovata was identified as a new mangrove species differentiated from Kandelia candel. However, little is known about their chloroplast (cp) genome differences and their possible ecological significance. In this study, 25 whole cp genomes, with seven samples of K. candel from Malaysia, Thailand, and Bangladesh and 18 samples of K. obovata from China, were sequenced for comparison. The cp genomes of both species encoded 128 genes, namely 83 protein-coding genes, 37 tRNA genes, and eight rRNA genes, but the cp genome size of K. obovata was ~2 kb larger than that of K. candle due to the presence of more and longer repeat sequences. Of these, tandem repeats and simple sequence repeats exhibited great differences. Principal component analysis based on indels, and phylogenetic tree analyses constructed with homologous protein genes from the single-copy genes, as well as 38 homologous pair genes among 13 mangrove species, gave strong support to the separation of the two species within the Kandelia genus. Homologous genes ndhD and atpA showed intraspecific consistency and interspecific differences. Molecular dynamics simulations of their corresponding proteins, NAD(P)H dehydrogenase chain 4 (NDH-D) and ATP synthase subunit alpha (ATP-A), predicted them to be significantly different in the functions of photosynthetic electron transport and ATP generation in the two species. These results suggest that the energy requirement was a pivotal factor in their adaptation to differential environments geographically separated by the South China Sea. Our results also provide clues for future research on their physiological and molecular adaptation mechanisms to light and temperature.

In the presented study, a combined physiology, proteomics and gene expression study was performed using P. massoniana seedlings cultivated at various calcium levels. The aim of the study is to investigate the impacts of exogenous calcium on P. massoniana seedling growth and development and to reveal the underlying molecular mechanisms. The results showed that calcium deficiency lead to severe seedling growth and development inhibition while adequate exogenous calcium markedly improved the growth and development. The underlying mechanisms involved diverse calcium influenced biological processes and metabolism pathways including photosynthesis, carbohydrate metabolism and energy production, protein metabolism, secondary metabolism and calcium signal transduction and calcium ion homeostasis. In general, calcium deficiency inhibited or impaired these pathways and processes, while sufficient exogenous calcium improved and benefited these cellular events through regulating a number of related enzymes and proteins. Besides, adequate exogenous calcium supply relieved oxidation stress which occurred at low calcium level. Enhanced cell wall formation and consolidation and cell division also play a role in exogenous calcium improved P. massoniana seedling growth and development. Our study facilitates the elucidation of the potential regulatory role of calcium in P. massoniana physiology and biology and is of guiding significance in pinaceae plants forestry.

Spartina alterniflora is rapidly spreading along the southeast coast of China as an invasive species. However, the molecular mechanism of its adaptation via high tillering to salt environment is unclear yet. The objective of this study is to investigate the effect of salinity on the underlying mechanism of strigolactone (SLs) signaling-mediated tillering in S. alterniflora. The field transplant and greenhouse experiments were set up, while the tillering processes under different salinities were measured. The results showed that moderate (13-18‰, 15‰) salinity promoted the outgrowth of S. alterniflora tiller than control (0-6‰, 0‰) and high salinity (29-32‰, 30‰). Furthermore, the content of strigolactones (SLs) and the genes involved in SLs biosynthesis (D10, D17) ＆ signaling (D14, D53) were analyzed on the seedlings grown in greenhouse. The SLs content in roots was reduced with the increase of salinity, which resulted from the down-regulation of SaD10 and SaD17 expression. In addition, moderate salinity (15‰) down-regulated SaD14 and up-regulated SaD53 expression, while these gene expressions exhibited different under the control salinity (0‰) and high salinity (30‰). In conclusion, our data revealed that 15‰ salinity promoted the tillering process by depressing the SLs level via inhibiting SLs biosynthesis and perception, but activating the expression of a repressor in SLs signaling in S. alterniflora. The conclusion can help us to understand the mechanism of fast invasion of S. alterniflora into new intertidal salt habitats.