Efficacy of insect-resistance Bt/Cp TI transgenes in F5–F7generations of rice crop–weed hybrid progeny: implications for assessing ecological impact of transgene flow

Ecological impact of transgene flow into populations of wild/weedy relatives is associated with fitness effects in hybrid progeny. Most studies assessing fitness effects focus essentially on early-generation hybrid progeny. However, whether the transgenes remain effective and durable in advanced generations of hybrid progeny remains unclear. We conducted a common garden experiment with F5–F7hybrid progeny derived from crosses between insect-resistant transgenic(Bt/Cp TI) rice and weedy rice, to examine their insect resistance and fitness effects of transgenes on progeny. Hybrid progeny were grown under different insect pressures and cultivation modes where insect damage and fitness-related traits were measured in the same growth season. Plants with transgenes showed significantly lower insect damage(10 % vs.32 %) and higher fecundity(551 vs. 392 seeds/plant) than those without transgenes in F5–F7populations, suggesting the efficacy of transgenes for insect resistance. Fitness benefits of the transgenes were similar among the F5–F7populations, indicating the stability of transgenic effects. A positive correlation between insect index and fecundity change was detected, stressing the important role of ambient insect pressures in assessing fitness effects caused by insect-resistance transgenes. Our results have importantimplications for assessing ecological impacts caused by transgene flow to wild/weedy relatives. For cost-effectiveness, the experimental estimation of fitness effects is probably sufficient based on data from hybrids in early generations. Given that fitness effects of insect-resistance transgenes are associated with ambient insect pressure,ecological risk assessment on transgene flow should consider this variable in experimental design, reasonably reflecting actual situations in wild/weedy populations.

Limited ecological risk of insect-resistance transgene flow from cultivated rice to its wild ancestor based on life-cycle fitness assessment

Ecological impact caused by transgene flow from genetically engineered(GE) crops to their wild relatives is largely determined by the fitness effect brought by a transgene. To estimate such impact is critical for the ecological risk assessment prior to the commercialization of GE crops. We produced F1 and F2hybrid descendants from crosses of two insect-resistant GE rice lines(Bt, Bt/Cp TI)and their non-GE rice parent with a wild rice(Oryza rufipogon) population to estimate the transgenic fitness. Insect damages and life-cycle fitness of GE and non-GE crop–wild hybrid descendants as well as their wild parent were examined in a common-garden experiment. No significant differences in insect damages were observed between the wild rice parent and GE hybrid descendants under highinsect pressure. The wild parent showed significantly greater relative survival-regeneration ratios than its GE and non-GE hybrid descendants under both high- and low-insect pressure. However, more seeds were produced in GE hybrid descendants than their non-GE counterparts under high-insect pressure. Given that the introduction of Bt and Bt/Cp TI transgenes did not provide greater insect resistance to crop–wild hybrid descendants than their wild parent, we predict that transgene flow from GE insect-resistant rice to wild rice populations may not cause considerable ecological risks.

Population Genetic Structure of the Medicinal Plant Vitex rotundifolia in China: Implications for its Use and Conservation

Vitex rotundifolia L. is an important plant species used in traditional Chinese medicine. For its efficient use and conservation, genetic diversity and clonal variation of V. rotundifolia populations in China were investigated using inter-simple sequence repeat markers. Fourteen natural populations were included to estimate genetic diversity, and a large population with 135 individuals was used to analyze clonal variation and fine-scale spatial genetic structure. The overall genetic diversity （GD） of V. rotundifolia populations in China was moderate （GD=0.190）, with about 40% within-population variation. Across all populations surveyed, the average within-population diversity was moderate （P = 22.6%; GD = 0.086）. A relatively high genetic differentiation （Gst = 0.587） among populations was detected based on the analysis of molecular variance data. Such characteristics of V. rotundifofia are likely attributed to its sexual/asexual reproduction and limited gene flow. The genotypic diversity （D = 0.992） was greater than the average values of a clonal plant, indicating its significant reproduction through seedlings. Spatial autocorrelation analysis showed a clear within-population structure with gene clusters of approximately 20 m. Genetic diversity patterns of V. rotundifolia in China provide a useful guide for its efficient use and conservation by selecting particular populations displaying greater variation that may contain required medicinal compounds, and by sampling individuals in a population at 〉20 m spatial intervals to avoid collecting individuals with identical or similar genotypes.

Strategic Conservation of Orchard Germplasm Based on Indigenous Knowledge and Genetic Diversity:a Case Study of Sour Orange Populations in China

To effectively conserve sour orange （Citrus aurantium L.） germplasm on two islands at the estuary of the Yangtze River in China, we estimated genetic variation and relationships of the known parental trees and their proposed descendents （young trees） using the fingerprints of random amplified polymorphic DNA （RAPD）. Results based on RAPD analyses showed considerable genetic diversity in the parental populations （He = 0.202）. The overall populations including the parental and young trees showed slightly higher genetic diversity （He = 0.298） than the parents, with about 10% variation between populations. An unweighted pair group method with arithmetic mean analysis dendrogram based on cluster analysis of the Jaccard similarity among individuals demonstrated a more complicated relationship of the parental and young trees from the two islands, although the young trees showed a clear association with parental trees. This indicates a significant contribution of parental trees in establishing the sour orange populations on the two islands. According to farmers＇ knowledge, conservation of only one or two parental trees would be sufficient because they believed that the whole populations were generated from a single mother tree. However, this study suggests that preserving most parental trees and some selected young trees with distant genetic relationships should be an effective conservation strategy for sour orange germplasm on the two islands.

A conserved unusual posttranscriptional processing mediated by short,direct repeated (SDR) sequences in plants

In several stress responsive gene loci of monocot cereal crops,we have previously identified an unusual posttranscriptional processing mediated by paired presence of short direct repeated （SDR） sequences at 5＇ and 3＇ splicing junctions that are distinct from conventional （U2/U12-type） splicing boundaries.By using the known SDR-containing sequences as probes,24 plant candidate genes involved in diverse functional pathways from both monocots and dicots that potentially possess SDR-mediated posttranscriptional processing were predicted in the GenBank database.The SDRs-mediated posttranscriptional processing events including cis-and trans-actions were experimentally detected in majority of the predicted candidates.Extensive sequence analysis demonstrates several types of SDR-associated splicing peculiarities including partial exon deletion,exon fragment repetition,exon fragment scrambling and trans-splicing that result in either loss of partial exon or unusual exonic sequence rearrangements within or between RNA molecules.In addition,we show that the paired presence of SDR is necessary but not sufficient in SDR-mediated splicing in transient expression and stable transformation systems.We also show prokaryote is incapable of SDR-mediated premRNA splicing.

Dr, Yang Zhong： An explorer on the roac Forever

On the morning of September 25th 2017, grievous news spread from the remote Ordos region of Inner Mongolia to Fudan University campus in Shanghai. Professor Yang Zhong （Fig. 1）, a famous botanist and the Dean of Fudan University＇s graduate school, passed away in a tragic car accident while on a business trip.