MePP2C24, a cassava (Manihot esculenta) gene encoding protein phosphatase 2C, negatively regulates drought stress and abscisic acid responses in transgenic Arabidopsis thaliana.

Abscisic acid (ABA) signaling plays a crucial role in plant development and response to abiotic/biotic stress. However, the function and regulation of protein phosphatase 2C (PP2C), a key component of abscisic acid signaling, under abiotic stress are still unknown in cassava, a drought-tolerant crop. In this study, a cassava PP2C gene (MePP2C24) was cloned and characterized. The MePP2C24 transcripts increased in response to mannitol, NaCl, and ABA. Overexpression of MePP2C24 in Arabidopsis resulted in increased sensitivity to drought stress and decreased sensitivity to exogenous ABA. This was demonstrated by transgenic lines having higher levels of malondialdehyde (MDA), ion leakage (IL), and reactive oxygen species (ROS), lower activities of catalase (CAT) and peroxidase (POD), and lower proline content than wild type (WT) under drought stress. Moreover, MePP2C24 overexpression caused decrease in expression of drought-responsive genes related to ABA signaling pathway. In addition, MePP2C24 was localized in the cell nucleus and showed self-activation. Furthermore, many MePYLs (MePYL1, MePYL4, MePYL7-9, and MePYL11-13) could interact with MePP2C24 in the presence of ABA, and MePYL1 interacted with MePP2C24 in both the presence and absence of ABA. Additionally, MebZIP11 interacted with the promoter of MePP2C24 and exerted a suppressive effect. Taken together, our results suggest that MePP2C24 acts as a negative regulator of drought tolerance and ABA response.

Metabolic GWAS-based dissection of genetic basis underlying nutrient quality variation and domestication of cassava storage root.

BACKGROUND: Metabolites play critical roles in regulating nutritional qualities of plants, thereby influencing their consumption and human health. However, the genetic basis underlying the metabolite-based nutrient quality and domestication of root and tuber crops remain largely unknown. RESULTS: We report a comprehensive study combining metabolic and phenotypic genome-wide association studies to dissect the genetic basis of metabolites in the storage root (SR) of cassava. We quantify 2,980 metabolic features in 299 cultivated cassava accessions. We detect 18,218 significant marker-metabolite associations via metabolic genome-wide association mapping and identify 12 candidate genes responsible for the levels of metabolites that are of potential nutritional importance. Me3GT, MeMYB4, and UGT85K4/UGT85K5, which are involved in flavone, anthocyanin, and cyanogenic glucoside metabolism, respectively, are functionally validated through in vitro enzyme assays and in vivo gene silencing analyses. We identify a cluster of cyanogenic glucoside biosynthesis genes, among which CYP79D1, CYP71E7b, and UGT85K5 are highly co-expressed and their allelic combination contributes to low linamarin content. We find MeMYB4 is responsible for variations in cyanidin 3-O-glucoside and delphinidin 3-O-rutinoside contents, thus controlling SR endothelium color. We find human selection affects quercetin 3-O-glucoside content and SR weight per plant. The candidate gene MeFLS1 is subject to selection during cassava domestication, leading to decreased quercetin 3-O-glucoside content and thus increased SR weight per plant. CONCLUSIONS: These findings reveal the genetic basis of cassava SR metabolome variation, establish a linkage between metabolites and agronomic traits, and offer useful resources for genetically improving the nutrition of cassava and other root crops.