Comparative analysis of cold-responsive genes under short-term cold stimulation and cold-adaptive genes under long-term heterogeneous environments reveals a cold adaptation mechanism in weeping forsythia.

Identifying cold-related genes can provide insights into the cold adaptation mechanism of weeping forsythia. In this study, we compared the changes in gene expressions and physiological and biochemical indices under short-term cold stimulation with the changes in gene sequences under a long-term heterogeneous environment to investigate the cold adaptation mechanism in weeping forsythia. The data of adaptive gene sequence changes, e.g., single nucleotide polymorphisms, were obtained from previous landscape genomics studies. The physiological and biochemical indicators and transcriptome results showed that weeping forsythia initiated a series of programs, including increasing cell osmotic pressures, scavenging ROS, activating the defense mechanism that crosses with pathogen infection, and upregulating CBF/DREB1 transcription factor 1, to cope with short-term cold stress. A reanalysis of landscape genomic data suggested that weeping forsythia responded to long-term heterogeneous cold stress by the differentiation of genes related to synthesis of aromatic substances and adenosine triphosphate. Our results supported the hypothesis that the adaptation mechanisms of species to short-term environmental stimulation and long-term stress in heterogeneous environments are different. The differences in cold tolerance among populations are not necessarily obtained by changing cold-responsive gene sequences. This study provides new insights into the cold adaptation mechanisms of plants.

Molecular characterization of putative vacuolar NHX-type Na(+)/H(+) exchanger genes from the salt-resistant tree Populus euphratica.

The vacuolar NHX-type Na(+)/H(+) exchangers play a key role in salt tolerance in plants. However, little is known about the Na(+)/H(+) exchangers in the salt-resistant tree, Populus euphratica. In this study, we identified six putative vacuolar Na(+)/H(+) exchanger genes from P. euphratica, designated as PeNHX1-6. Real-time polymerase chain reaction indicated that the PeNHX1/3/6 transcripts were abundant compared with the other three PeNHX genes in the three tissues (roots, stems and leaves) examined. After NaCl treatment for 6 h, the transcript levels of PeNHX1-6 were upregulated in the roots. To address the function of PeNHX1-6, complementation studies were performed with the salt-sensitive yeast mutant strain R100, which lacks activity of the endosomal Na(+)/H(+) antiporter NHX1. The results showed that PeNHX1-6 compensates, at least in part, for the function of yeast NHX1. Moreover, PeNHX3 was targeted to the tonoplast when transiently expressed in onion. Together, these results suggest that PeNHX1-6 function as vacuolar Na(+)/H(+) exchangers and that PeNHX products play an important role in the salt resistance of P. euphratica.