Cassava starch is a widely used raw material for industrial production. South Chinese cassava cultivar 8 (Manihot esculenta Crantz cv. SC8) is one of the main locally planted cultivars. In this study, an efficient transformation system for cassava SC8 mediated with Agrobacterium strain LBA4404 was presented for the first time. Cassava friable embryogenic calli (FECs) were transformed through the binary vector pCAMBIA1304 harboring GUS- and GFP-fused genes driven by the CaMV35S promoter. The transformation efficiency was increased in the conditions of Agrobacterium strain cell infection density (OD600 = 0.65), 250 µM acetosyringone induction, and agro-cultivation with wet FECs for 3 days in dark. Based on the optimized transformation protocol, approximately 120–140 independent transgenic lines per mL settled cell volume (SCV) of FECs were created by gene transformation in approximately 5 months, and 45.83% homozygous mono-allelic mutations of the MePDS gene with a YAO promoter-driven CRISPR/Cas9 system were generated. This study will open a more functional avenue for the genetic improvement of cassava SC8.

Editing of the promoter in the disease-susceptibility gene MeSWEET10a of SC8 cassava confers resistance to cassava bacterial blight (CBB). All mutated cassava lines had normal morphological and yield-related traits as the wild type. The results lay a research foundation for breeding cassava resistant to bacterial blight.

Plant pectin methylesterases (PMEs) play crucial roles in regulating cell wall modification and response to various stresses. Members of the PME family have been found in several crops, but there is a lack of research into their presence in cassava (Manihot esculent), which is an important crop for world food security. In this research, 89 MePME genes were identified in cassava that were separated into two types (type-Ⅰ and type-Ⅱ) according to the existence or absence of a pro-region (PMEI domain). The MePME gene members were unevenly located on 17 chromosomes, with 19 gene pairs being identified that most likely arose via duplication events. The MePMEs could be divided into ten sub-groups in type-Ⅰ and five sub-groups in type-Ⅱ. The motif analysis revealed 11 conserved motifs in type-Ⅰ and 8 in type-Ⅱ MePMEs. The number of introns in the CDS region of type-Ⅰ MePMEs ranged between one and two, and the number of introns in type-Ⅱ MePMEs ranged between one and nine. There were 21 type-Ⅰ and 31 type-Ⅱ MePMEs that contained signal peptides. Most of the type-Ⅰ MePMEs had two conserved “RK/RLL” and one “FPSWVS” domain between the pro-region and the PME domain. Multiple stress-, hormone- and tissue-specific-related cis-acting regulatory elements were identified in the promoter regions of MePME genes. A total of five co-expressed genes (MePME1, MePME2, MePME27, MePME65 and MePME82) were filtered from different abiotic stresses via the use of UpSet Venn diagrams. The gene expression pattern analysis revealed that the expression of MePME1 was positively correlated with the degree of cassava postharvest physiological deterioration (PPD). The expression of this gene was also significantly upregulated by 7% PEG and 14 °C low-temperature stress, but slightly downregulated by ABA treatment. The tissue-specific expression analysis revealed that MePME1 and MePME65 generally displayed higher expression levels in most tissues than the other co-expressed genes. In this study, we obtain an in-depth understanding of the cassava PME gene family, suggesting that MePME1 could be a candidate gene associated with multiple abiotic tolerance.

Potato (Solanum tuberosum L.) cv. Eshu 10 was used to investigate the effects of exogenous gibberellic acid (GA3), abscisic acid (ABA), and low-temperature stress on changes of hormone content, expression patterns of StTCP15 gene, and tuber dormancy characteristics. Under GA3 treatment and low-temperature stress, tuber dormancy was broken in about one week sooner compared with the control group, but ABA treatment did not significantly promote the breaking of tuber dormancy. The results of hormone determination using liquid chromatography-mass spectrometry (LC-MS/ MS) showed that the content of ABA in tubers treated with GA3 or low-temperature stress was lower than in the control group, and it was higher than in the control group under ABA treatment. The GA3 content of tubers was higher than in the control group under GA3 treatment and lower under low-temperature stress. During dormancy, the ABA content continued to increase and GA3 content fluctuated, ABA content rapidly decreased and GA3 content rapidly increased when the dormancy was breaking, and both ABA content and GA3 content increased during germination. The results from the assay of real-time quantitative PCR showed that the expression of the StTCP15 gene was continuously increased during the dormant period in all groups, and the expression of the StTCP15 gene was the highest at the time of dormancy release. The expression of the StTCP15 gene was increased about 15 times on the 7 th d under low-temperature stress and was restored at room temperature. Thus, the StTCP15 gene can respond to GA3, ABA, and low-temperature stress and may be involved in the release of potato tuber dormancy.