[CbCYP716A261, a New β-Amyrin 28-Hydroxylase Involved in Conyzasaponin Biosynthesis from Conyza blinii]

Conyzasaponins produced by the traditional Chinese herb Conyza blinii are oleanane-type saponins with a wide range of biological activities. Here, we identified a gene, designated CbCYP716A261, encoding a β-amyrin 28-hydroxylase in conyzasaponins biosynthesis. Ten full putative CYP sequences were isolated from Conyza blinii transcript tags. The CbCYP716A261 gene product was selected as the putative β-amyrin 28-hydroxylase by phylogenetic analysis and transcriptional activity analysis of methyl jasmonate-treated Conyza blinii. To identify the enzymatic activity, we performed enzymatic activity experiments in vitro and in vivo. The HPLC results revealed that CbCYP716A261 catalyzes the hydroxylation of β-amyrin at the C-28 position to yield oleanolic acid. Our findings provide new information about the conyzasaponin biosynthesis pathway and widen the list of isolated β-amyrin 28-hydroxylases.

Gene expression in response to glyphosate treatment in fleabane (Conyza bonariensis) - glyphosate death response and candidate resistance genes

BACKGROUND

This study takes a whole-transcriptome approach to assess gene expression changes in response to glyphosate treatment in glyphosate-resistant fleabane. We assessed gene expression changes in both susceptible and resistant lines so that the glyphosate death response could be quantified, and constitutively expressed candidate resistance genes identified. There are three copies of the glyphosate target site (5-enolpyruvylshikimate-3-phosphate; EPSPS) gene in Conyza and because Conyza bonariensis is allohexaploid, there is a baseline nine copies of the gene in any individual.

RESULTS

Many genes were differentially expressed in response to glyphosate treatment. Known resistance mutations are present in EPSPS2 but they are present in a glyphosate-susceptible line as well as resistant lines and therefore not sufficient to confer resistance. EPSPS1 is expressed four times more than EPSPS2, further reducing the overall contribution of these mutations.

CONCLUSION

We demonstrate that glyphosate resistance in C. bonariensis is not the result of EPSPS mutations or overexpression, but due to a non-target-site mechanism. A large number of genes are affected by glyphosate treatment. We present a list of candidate non-target-site-resistance (NTSR) genes in fleabane for future studies into these mechanisms. © 2017 Society of Chemical Industry.

Physiological Responses and Tolerance Mechanisms to Cadmium in Conyza canadensis

Experiments were conducted to examine the effects of different concentrations of Cd on the performance of the Cd accumulator Conyza canadensis. Cd accumulation in roots and leaves (roots>leaves) increased with increasing Cd concentration in soil. High Cd concentration inhibited plant growth, increased the membrane permeability of leaves, and caused a significant decline in plant height and chlorophyll [chlorophyll (Chl) a, Chl b, and total Chl] content. Leaf ultrastructural analysis of spongy mesophyllic cells revealed that excessive Cd concentrations cause adverse effects on the chloroplast and mitochondrion ultrastructures of C. canadensis. However, the activities of antioxidant enzymes, such as superoxide dismutase, catalase, peroxidase, total non-protein SH compounds, glutathione, and phytochelatin (PC) concentrations, showed an overall increase. Specifically, the increase in enzyme activities demonstrated that the antioxidant system may play an important role in eliminating or alleviating the toxicity of Cd in C. canadensis. Furthermore, results demonstrate that PC synthesis in plant cells is related to Cd concentration and that PC production levels in plants are related to the toxic effects caused by soil Cd level. These findings demonstrate the roles played by these compounds in supporting Cd tolerance in C. canadensis.