Comprehensive analysis of WOX transcription factors provide insight into genes related to the regulation of unisexual flowers development in Akebia trifoliata.

Akebia trifoliata is a fascinating economic and medicinal plant that produces functionally unisexual flowers due to stamen/pistil abortion during flower development, and the genetic regulation pathway of this process remain completely unknown. Here, 10 AktWOXs were identified for the first time, all contained a highly conserved homeodomain. AktWOXs were divided into three clades, each with the same or similar intron, exon, and motifs distribution. Many cis-elements related to stress response, growth and development, and hormone response were found in the AktWOXs promoter region. In addition, four candidate genes AktWOX8, AktWOX11, AktWOX13.2 and AktWUS that might be involved in unisexual flowers development were screened, all of which were located in the nucleus and showed transcriptional activation activity. Yeast one-hybrid showed that both AktKNU and AktAG1, the potential core transcription factors in the activity termination pathway of flower meristem stem cells, could bind to the promoter region of AktWUS. Dual-luciferase assay further confirmed that only AktKNU inhibited the expression of AktWUS. Collectively, this study revealed the mechanism of AktWUS that might affect the formation of unisexual flowers by regulating the timely termination of flower meristem in A. trifoliata.

Evidence for two types of Aquilegia ecalcarata and its implications for adaptation to new environments.

Spurs have played an important role in the radiation of the genus Aquilegia, but little is known about how the spurless state arose in A. ecalcarata. Here we aim to characterize the genetic divergence within A. ecalcarata and gain insights into the origin of this species. A total of 19 populations from A. ecalcarata and 23 populations from three of its closest relatives (Aquilegia kansuensis, Aquilegia rockii and Aquilegia yabeana) were sampled in this study. We sequenced fifteen nuclear gene fragments across the genome and three chloroplast loci to conduct phylogenetic, PCoA and STRUCTURE analyses. Our analyses indicate that A. ecalcarata may not be monophyletic and can be divided into two distinct lineages (A. ecalcarata I and A. ecalcarata II). A. ecalcarata I is genetically close to A. kansuensis, whereas A. ecalcarata II is close to A. rockii. Isolation-with-migration analysis suggested that historical gene flow was low between A. ecalcarata I and A. rockii, as well as between A. ecalcarata II and A. kansuensis. The two distinct lineages of A. ecalcarata show significant divergence in 13 floral traits and also have distinct distributions. In addition, both A. ecalcarata I and II are adapted to a stony environment that differs from that of their closest relatives, indicating a habitat shift may have driven new adaptations. Our findings enrich the understanding of how floral evolution contributes to species diversification.

Divergence in the Aquilegia ecalcarata complex is correlated with geography and climate oscillations: Evidence from plastid genome data.

Quaternary climate oscillations and geographical heterogeneity play important roles in determining species and genetic diversity distribution patterns, but how these factors affect the migration and differentiation of East Asian plants species at the population level remains poorly understood. The Aquilegia ecalcarata complex, a group that originated in the Late Tertiary and is widely distributed throughout East Asia, displays high genetic variation that is suitable for studying elaborate phylogeographic patterns and demographic history related to the impact of Quaternary climate and geography. We used plastid genome data from 322 individuals in 60 populations of the A. ecalcarata complex to thoroughly explore the impact of Quaternary climate oscillations and geography on the phylogeographic patterns and demographic history of the A. ecalcarata complex through a series of phylogenetic, divergence time estimation, and demographic history analyses. The dry, cold climate and frequent climate oscillations that occurred during the early Pleistocene and the Mid-Pleistocene transition led to the differentiation of the A. ecalcarata complex, which was isolated in various areas. Geographically, the A. ecalcarata complex can be divided into Eastern and Western Clades and five subclades, which conform to the divergence of the East Asian flora. Our results clearly show the impact of Quaternary climate and geography on evolutionary history at the population level. These findings promote the understanding of the relationship between plant genetic differentiation and climate and geographical factors of East Asia at the population level.

The dispersal-related traits of an invasive plant Galinsoga quadriradiata correlate with elevation during range expansion into mountain ranges.

Detecting shifts in trait values among populations of an invasive plant is important for assessing invasion risks and predicting future spread. Although a growing number of studies suggest that the dispersal propensity of invasive plants increases during range expansion, there has been relatively little attention paid to dispersal patterns along elevational gradients. In this study, we tested the differentiation of dispersal-related traits in an invasive plant, Galinsoga quadriradiata, across populations at different elevations in the Qinling and Bashan Mountains in central China. Seed mass-area ratio (MAR), an important seed dispersal-related trait, of 45 populations from along an elevational gradient was measured, and genetic variation of 23 populations was quantified using inter-simple sequence repeat (ISSR) markers. Individuals from four populations were then planted in a greenhouse to compare their performance under shared conditions. Changing patterns of seed dispersal-related traits and populations genetic diversity along elevation were tested using linear regression. Mass-area ratio of G. quadriradiata increased, while genetic diversity decreased with elevation in the field survey. In the greenhouse, populations of G. quadriradiata sourced from different elevations showed a difference response of MAR. These results suggest that although rapid evolution may contribute to the range expansion of G. quadriradiata in mountain ranges, dispersal-related traits will also likely be affected by phenotypic plasticity. This challenges the common argument that dispersal ability of invasive plants increases along dispersal routes. Furthermore, our results suggest that high-altitude populations would be more effective at seed dispersal once they continue to expand their range downslope on the other side. Our experiment provides novel evidence that the spread of these high-altitude populations may be more likely than previously theorized and that they should thus be cautiously monitored.

The cold response regulator CBF1 promotes Arabidopsis hypocotyl growth at ambient temperatures.

Light and temperature are two core environmental factors that coordinately regulate plant growth and survival throughout their entire life cycle. However, the mechanisms integrating light and temperature signaling pathways in plants remain poorly understood. Here, we report that CBF1, an AP2/ERF-family transcription factor essential for plant cold acclimation, promotes hypocotyl growth under ambient temperatures in Arabidopsis. We show that CBF1 increases the protein abundance of PIF4 and PIF5, two phytochrome-interacting bHLH-family transcription factors that play pivotal roles in modulating plant growth and development, by directly binding to their promoters to induce their gene expression, and by inhibiting their interaction with phyB in the light. Moreover, our data demonstrate that CBF1 promotes PIF4/PIF5 protein accumulation and hypocotyl growth at both 22°C and 17°C, but not at 4°C, with a more prominent role at 17°C than at 22°C. Together, our study reveals that CBF1 integrates light and temperature control of hypocotyl growth by promoting PIF4 and PIF5 protein abundance in the light, thus providing insights into the integration mechanisms of light and temperature signaling pathways in plants.

Natural variation of C-repeat-binding factor (CBFs) genes is a major cause of divergence in freezing tolerance among a group of Arabidopsis thaliana populations along the Yangtze River in China.

We used a monophyletic group of four natural populations of Arabidopsis thaliana expanded from a single ancestor along the Yangtze River c. 90,000 yr ago to study the molecular mechanism of the divergence in their freezing tolerance, in order to gain an insight into the genetic basis of their local adaption to low temperatures. Freezing tolerance assays, measurements of metabolites in the raffinose biosynthesis pathway and transactivation-activity assays of variation in forms of cold-responsive transcription factors were conducted on the four populations. Quantitative trait locus mapping was adopted with F2 populations of the most- and least freezing-tolerant populations. The degree of freezing tolerance among the four populations was negatively correlated with the lowest monthly average temperature of January in their native habitats, and positively correlated to the expression level of some cold-regulated genes. We identified a major locus harboring three cold-responsive transcription factor genes CBF1-3, and found a nucleotide insertion in CBF2 in all populations except SXcgx, which generated a dysfunctional CBF2 protein. The CBF2 in SXcgx experienced a stronger natural selection in the cooler environment after CBF3 lost its response to low temperature, which possibly reflects a local adaptation of these populations during the expansion from a common ancestor.

AtMYB14 Regulates Cold Tolerance in Arabidopsis.

Low temperature affects plant growth and crop productivity. The CBF genes are a class of transcription factors that play important roles in cold response. Here we report that AtMYB14 participates in freezing tolerance in Arabidopsis by affecting expression of CBF genes. The AtMYB14 gene was down-regulated by cold treatment. AtMYB14 encodes a nuclear protein that functions as an R2R3-MYB transcription activator. Knock-down of AtMYB14 by artificial microRNA increased the tolerance to freezing stress. Both the CBF genes and the downstream genes were induced to a much higher level in AtMYB14 knock-down plants than in wild type under cold treatment. Our results suggest that AtMYB14 plays an important role in the plant response to cold stress.

The origin of populations of Arabidopsis thaliana in China, based on the chloroplast DNA sequences.

BACKGROUND: In the studies incorporating worldwide sampling of A. thaliana populations, the samples from East Asia, especially from China, were very scattered; and the studies focused on global patterns of cpDNA genetic variation among accessions of A. thaliana are very few. In this study, chloroplast DNA sequence variability was used to infer phylogenetic relationships among Arabidopsis thaliana accessions from around the world, with the emphasis on samples from China. RESULTS: A data set comprising 77 accessions of A. thaliana, including 19 field-collected Chinese accessions together with three related species (A. arenosa, A. suecica, and Olimarabidopsis cabulica) as the out-group, was compiled. The analysis of the nucleotide sequences showed that the 77 accessions of A. thaliana were partitioned into two major differentiated haplotype classes (MDHCs). The estimated divergence time of the two MDHCs was about 0.39 mya. Forty-nine haplotypes were detected among the 77 accessions, which exhibited nucleotide diversity (pi) of 0.00169. The Chinese populations along the Yangtze River were characterized by five haplotypes, and the two accessions collected from the middle range of the Altai Mountains in China shared six specific variable sites. CONCLUSIONS: The dimorphism in the chloroplast DNA could be due to founder effects during late Pleistocene glaciations and interglacial periods, although introgression cannot be ruled out. The Chinese populations along the Yangtze River may have dispersed eastwards to their present-day locations from the Himalayas. These populations originated from a common ancestor, and a rapid demographic expansion began approximately 90,000 years ago. Two accessions collected from the middle range of the Altai Mountains in China may have survived in a local refugium during late Pleistocene glaciations. The natural populations from China with specific genetic characteristics enriched the gene pools of global A. thaliana collections.