Overexpression of leucoanthocyanidin reductase or anthocyanidin reductase elevates tannins content and confers cassava resistance to two-spotted spider mite.

The two-spotted spider mite (TSSM) is a destructive cassava pest. Intensive demonstration of resistance mechanism greatly facilitates the creation of TSSM-resistant cassava germplasm. Gene to metabolite network plays a crucial role in modulating plant resistance, but little is known about the genes and related metabolites which are responsible for cassava resistance to TSSM. Here, a highly resistant (HR) and a highly susceptible (HS) cassava cultivar were used, integrative and comparative transcriptomic and metabolomic analyses between these two cultivars after TSSM infestation revealed that several genes and metabolites were closely related and significantly different in abundance. In particular, the expression of leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) genes showed a high positive correlation with most of the metabolites in the tannin biosynthesis pathway. Furthermore, transgenic cassava lines overexpressing either of the genes elevated tannin concentrations and conferred cassava resistance to TSSM. Additionally, different forms of tannins possessed distinct bioactivity on TSSM, of which total condensed tannins (LC50 = 375.68 mg/l) showed maximum lethal effects followed by procyanidin B1 (LC50 = 3537.10 mg/l). This study accurately targets LAR, ANR and specific tannin compounds as critical genes and metabolites in shaping cassava resistance to TSSM, which could be considered as biomarkers for evaluation and creation of pest-resistant cassava germplasm.

Reference Gene Selection for Analyzing the Transcription Patterns of Two Fatty Acyl-CoA Reductase Genes From Paracoccus marginatus (Hemiptera: Pseudococcidae).

Paracoccus marginatus (Hemiptera: Pseudococcidae), known as the papaya mealybug, could cause considerable yield loss of several plants. To date, there is no molecular-based study of P. marginatus. Fatty acyl-CoA reductases (FARs) are key enzymes involved in wax synthesis. In the present study, we cloned and characterized coding sequences (CDS) of two FAR genes from P. marginatus. The results showed that PmFAR1 and PmFAR2 CDS were 1,590 and 1,497 bp in length, respectively, and sequence analysis indicated that these two genes both had the conservative motifs belonging to FAR_C superfamily. Furthermore, seven candidate reference genes were analyzed for their expression stability by using common algorithms including comparative ΔCq method, geNorm, NormFinder, BestKeeper, and RefFinder. Eventually, ß-actin and GAPDH were the best reference genes in evaluating the expression of those two FAR genes. We found that PmFAR1 and PmFAR2 showed distinct expression patterns in different life stages. Moreover, the transcription of PmFAR1 and PmFAR2 in P. marginatus fed on resistant cassava cultivars was significantly lower compared with those fed on susceptible ones, indicating the potential function of FAR genes in cassava resistance to P. marginatus. The present study might help in better understanding the molecular mechanism of cassava resistance to mealybug.