Comparative transcriptome analysis of Saposhnikovia divaricata to reveal drought and rehydration adaption strategies.

BACKGROUND: Water scarcity has become one of the most prevalent environmental factors adversely affecting plant growth and development. Different species have developed multiple ways of drought resistance. Saposhnikovia divaricata is a commonly used traditional herb in East Asia. However, limited information is available on the drought response of this herb and further clarification of underlying molecular mechanism remains a challenge. METHODS AND RESULTS: In this study, a comparative transcriptome analysis was firstly conducted to identify the major pathways and candidate genes involved in the drought adaptive response of S. divaricata. The seedlings of S. divaricata were subjected to progressive drought by withholding water for 16 days followed by 8 days of rehydration. Transcriptome analysis identified a total of 89,784 annotated unigenes. The number of differentially expressed genes (DEGs) gradually increased with the deepening of drought and decreased after rehydration. Gene Ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis suggested genes related to oxidoreductase activity, carbohydrate metabolism, plant hormone signaling pathway and secondary metabolism were important in drought response of S. divaricata. Specific genes involved in reactive oxygen species scavenging system (POD, Cu/Zn-SOD, APX), abscisic acid and jasmonic acid signaling pathway (PYL4, PP2Cs, JAR1, JAZ) and phenylpropanoid biosynthesis (4CL, CCR, CAD) underwent dynamic alterations under drought and rehydration. Finally, the expression pattern of 12 selected DEGs from the transcriptomic profiling was validated by real-time quantitative PCR. CONCLUSION: Our study laid a foundation for understanding the stress response of S. divaricata and other Apiaceae family plant at molecular level.

Differential Expression of Calycosin-7-O-ß-D-glucoside Biosynthesis Genes and Accumulation of Related Metabolites in Different Organs of Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao Under Drought Stress.

Calycosin-7-O-ß-D-glycoside (CG), as a flavonoid, plays an important role in the abiotic stress response of Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao (A. mongholicus). CG is also an active ingredient in A. mongholicus with high medicinal value. However, the response mechanism of the CG biosynthetic pathway of drought stress is not clear. In this research, drought stress was inflicted upon A. mongholicus, and the variations in flavonoid metabolites and the correlating gene expression in CG biosynthesis were studied in roots, stems, and leaves of A. mongholicus by UHPLC-MRM-MS/MS and qRT-PCR. Drought stress reduced the dry weight and increased the content of malondialdehyde (MDA) and proline. Drought was beneficial to the accumulation of L-phenylalanine and 4-coumaric acid in leaves and promoted the accumulation of all target compounds in the roots, except calycosin. Overexpression of AmIOMT was observed in the leaves, but the content of formononetin which is the product of isoflavone O-methyltransferase (IOMT) catalysis was higher in stems than in leaves. This research aims to further understand the acclimation of abiotic stress and the regulation mechanism of flavonoid accumulation in A. mongholicus.

Solvent-Controlled C2/C5-Regiodivergent Alkenylation of Pyrroles.

A solvent-controlled C2/C5-selective alkenylation of 3,4-disubstituted pyrroles has been developed. The C3 substituent of pyrroles proved crucial to the regioselectivity. Substrates bearing directing groups at the C3 position exhibited excellent C2-selectivities in chelation-assisted CH activation in toluene or 1,4-dioxane. However, a DMSO/DMF solvent system could override the chelation effect of weak directing groups, such as carboxylate and carbonyl groups, favoring instead regioselectivity towards the more electron-rich C5 position. A series of 3-carboxylate and 3-carbonyl pyrroles were tested and showed moderate to good yields with good regioselectivities for both C2- and C5-alkenylation process.

Solvent-controlled switchable C-H alkenylation of 4-aryl-1H-pyrrole-3-carboxylates: application to the total synthesis of (±)-rhazinilam.

A solvent-controlled switchable C-H alkenylation of 4-aryl-1H-pyrrole-3-carboxylates via a Pd(OAc)2 catalyzed oxidative Heck reaction was first realized. The corresponding C2 and C5 alkenylation products were obtained in good yields with high regioselectivities, respectively. The selective C5-alkenylation was successfully applied to the total synthesis of (±)-rhazinilam.