Cloning and functional validation of molybdenum cofactor sulfurase gene from Ammopiptanthus nanus

Marker-Assisted Backcross Breeding of Drought-Tolerant Maize Lines Transformed by Vacuolar H+-Pyrophosphatase Gene (AnVP1) from Ammopiptanthus nanus

Maize is highly sensitive to water deficit but has high transpiration and biomass production, leading to a substantial water demand. Genetic engineering can overcome reproductive isolation and utilize drought-tolerant genes from distant species. Ammopiptanthus nanus is a relic of the Tertiary glaciation that can adapt to harsh environmental conditions. In our previous study, five maize homozygous T8 lines overexpressing the AnVP1 gene from Ammopiptanthus nanus were generated and showed the enhancement of drought tolerance. However, the recipient inbred line Zh-1 was poor in yield and agronomic performance. In the present study, the AnVP1 gene was backcrossed from donor parent L10 (one of the five T8 lines) into recurrent parent Chang 7-2 (one of the elite parents of the commercial hybrid Zhengdan 958). In total, 103 InDel markers were developed and used for assisted background selection. After two generations of foreground selection through glufosinate spraying, the detection of CP4 EPSP MAb1 strips, and the PCR amplification of the AnVP1 gene, along with the similarity of agronomic traits to the recurrent parent, and background selection assisted by these InDel markers, the transgenic AnVP1 gene became homozygous in the BC2 lines. The average recovery rate of the genetic background of the recurrent parent reached 74.80% in the BC1 population and 91.93% in the BC2 population, respectively. The results of RT-PCR and RT-qPCR indicated the stable expression of the AnVP1 gene in the two ultimately selected BC2F3 lines, BC2-36-12 and BC2-5-15. The drought tolerance of these two BC2F3 lines were significantly improved compared to the recurrent parent Chang 7-2, as revealed by their wilting phenotype and survival rate of seedlings. This improvement was related to the enhancement of water-retention ability, as indicated by higher RWC and the reduction in damage, as shown by the decrease in REL, MDA, and H2O2 under drought stress. The result of field evaluation in two arid and semi-arid environments indicated that the drought tolerance of Chang 7-2 was significantly improved. This study suggests that the improved Chang 7-2 can be crossed with Zheng 58 to develop the transgenic commercial hybrid Zhengdan 958.

Identification of circular RNAs of Cannabis sativa L. potentially involved in the biosynthesis of cannabinoids

We identified circRNAs in the Cannabis sativa L. genome and examined their association with 28 cannabinoids in three tissues of C. sativa. Nine circRNAs are potentially involved in the biosynthesis of six cannabinoids. Cannabis sativa L. has been widely used in the production of medicine, textiles, and food for over 2500 years. The main bioactive compounds in C. sativa are cannabinoids, which have multiple important pharmacological actions. Circular RNAs (circRNAs) play essential roles in growth and development, stress resistance, and the biosynthesis of secondary metabolites. However, the circRNAs in C. sativa remain unknown. In this study, to explore the role of circRNAs in cannabinoid biosynthesis, we performed RNA-Seq and metabolomics analysis on the leaves, roots, and stems of C. sativa. We identified 741 overlapping circRNAs by three tools, of which 717, 16, and 8 circRNAs were derived from exonic, intronic, and intergenic, respectively. Functional enrichment analysis indicated that the parental genes (PGs) of circRNAs were enriched in many processes related to biological stress responses. We found that most of the circRNAs showed tissue-specific expression and 65 circRNAs were significantly correlated with their PGs (P < 0.05, |r|≥ 0.5). We also determined 28 cannabinoids by High-performance liquid chromatography-ESI-triple quadrupole-linear ion trap mass spectrometry. Ten circRNAs, including ciR0159, ciR0212, ciR0153, ciR0149, ciR0016, ciR0044, ciR0022, ciR0381, ciR0006, and ciR0025 were found to be associated with six cannabinoids by weighted gene co-expression network analysis. Twenty-nine of 53 candidate circRNAs, including 9 cannabinoids related were validated successfully using PCR amplification and Sanger sequencing. Taken together, all these results would help to enhance our acknowledge of the regulation of circRNAs, and lay the foundation for breeding new C. sativa cultivars with high cannabinoids through manipulating circRNAs.

Genome-Wide Identification and Expression Analyses of AnSnRK2 Gene Family under Osmotic Stress in Ammopiptanthus nanus

Sucrose non-fermenting-1 (SNF1)-related protein kinase 2’s (SnRK2s) are plant-specific serine/threonine protein kinases and play crucial roles in the abscisic acid signaling pathway and abiotic stress response. Ammopiptanthus nanus is a relict xerophyte shrub and extremely tolerant of abiotic stresses. Therefore, we performed genome-wide identification of the AnSnRK2 genes and analyzed their expression profiles under osmotic stresses including drought and salinity. A total of 11 AnSnRK2 genes (AnSnRK2.1-AnSnRK2.11) were identified in the A. nanus genome and were divided into three groups according to the phylogenetic tree. The AnSnRK2.6 has seven introns and others have eight introns. All of the AnSnRK2 proteins are highly conserved at the N-terminus and contain similar motif composition. The result of cis-acting element analysis showed that there were abundant hormone- and stress-related cis-elements in the promoter regions of AnSnRK2s. Moreover, the results of quantitative real-time PCR exhibited that the expression of most AnSnRK2s was induced by NaCl and PEG-6000 treatments, but the expression of AnSnRK2.3 and AnSnRK2.6 was inhibited, suggesting that the AnSnRK2s might play key roles in stress tolerance. The study provides insights into understanding the function of AnSnRK2s.

Identification and characterization of the rice pre-harvest sprouting mutants involved in molybdenum cofactor biosynthesis

In cereal crops, ABA deficiency during seed maturation phase causes pre-harvest sprouting (PHS), and molybdenum cofactor (MoCo) is required for ABA biosynthesis. Here, two rice PHS mutants F254 and F5-1 were characterized. In addition to the PHS, these mutants showed pleiotropic phenotypes such as twisting and slender leaves, and then died when the seedling developed to four or five leaves. Map-based cloning showed that OsCNX6 and OsCNX1 encoding homologs of MoaE and MoeA were responsible for F254 and F5-1 mutants, respectively. Genetic complementation indicated that OsCNX6 not only rescued the PHS and seedling lethal phenotype of the cnx6 mutant, but also recovered the MoCo-dependent enzyme activities such as xanthine dehydrogenase (XDH), aldehyde oxidase (AO), nitrate reductase (NR) and sulfite oxidase (SO). Expression pattern showed that OsCNX6 was richly expressed in seed during embryo maturation by quantitative reverse transcriptase PCR and RNA in situ hybridization. Furthermore, the OsCNX6 overexpression plants can significantly enhance the MoCo-dependent enzyme activities, and improved the osmotic and salt stress tolerance without unfavorable phenotypes. Collectively, these data indicated that OsCNX6 participated in MoCo biosynthesis, and is essential for rice development, especially for seed dormancy and germination, and OsCNX6 could be an effective target for improving abiotic stress tolerance in rice.

Overexpression of a phospholipase Dα gene from Ammopiptanthus nanus enhances salt tolerance of phospholipase Dα1-deficient Arabidopsis mutant

A phospholipase Dα gene ( AnPLDα ) was cloned from xerophytic desert plant Ammopiptanthus nanus and its overexpression enhanced salt tolerance of a PLDα1 deficient Arabidopsis mutant. Phospholipase Dα (PLDα) hydrolyzes phosphatidylcholine to produce phosphatidic acid, and plays crucial role in plant tolerance to abiotic stress. In this study, a phospholipase Dα gene (AnPLDα) was cloned from xerophyte Ammopiptanthus nanus by the methods of homologous cloning and rapid amplification of cDNA ends, and evaluated for its function in stress tolerance. The full-length cDNA was 2832 bp long, containing an open reading frame of 2427 bp that encodes 808 amino acids. The putative protein was predicted to be localized to the cytoplasm and this was confirmed by transient expression of a fluorescent fusion protein. The endogenous expression of the AnPLDα gene was induced by high salt, dehydration, cold and abscisic acid. The heterologous expression of the AnPLDα gene improved salt tolerance of an Arabidopsis pldα1 knocked out mutant, and positively regulated the expression of the AtABI, AtNCED, AtRD29A, AtRD29B and AtADH genes. Therefore, the AnPLDα gene was concluded to be involved in response to abiotic stress. The AnPLDα gene is a hopeful candidate for transgenic application to improve stress tolerance of commercial crops.