Overexpression of the GmEXPA1 gene reduces plant susceptibility to Meloidogyne incognita

Overexpression of Wild Soybean Expansin Gene GsEXLB14 Enhanced the Tolerance of Transgenic Soybean Hairy Roots to Salt and Drought Stresses

As a type of cell-wall-relaxing protein that is widely present in plants, expansins have been shown to actively participate in the regulation of plant growth and responses to environmental stress. Wild soybeans have long existed in the wild environment and possess abundant resistance gene resources, which hold significant value for the improvement of cultivated soybean germplasm. In our previous study, we found that the wild soybean expansin gene GsEXLB14 is specifically transcribed in roots, and its transcription level significantly increases under salt and drought stress. To further identify the function of GsEXLB14, in this study, we cloned the CDS sequence of this gene. The transcription pattern of GsEXLB14 in the roots of wild soybean under salt and drought stress was analyzed by qRT-PCR. Using an Agrobacterium rhizogenes-mediated genetic transformation, we obtained soybean hairy roots overexpressing GsEXLB14. Under 150 mM NaCl- and 100 mM mannitol-simulated drought stress, the relative growth values of the number, length, and weight of transgenic soybean hairy roots were significantly higher than those of the control group. We obtained the transcriptomes of transgenic and wild-type soybean hairy roots under normal growth conditions and under salt and drought stress through RNA sequencing. A transcriptomic analysis showed that the transcription of genes encoding expansins (EXPB family), peroxidase, H+-transporting ATPase, and other genes was significantly upregulated in transgenic hairy roots under salt stress. Under drought stress, the transcription of expansin (EXPB/LB family) genes increased in transgenic hairy roots. In addition, the transcription of genes encoding peroxidases, calcium/calmodulin-dependent protein kinases, and dehydration-responsive proteins increased significantly. The results of qRT-PCR also confirmed that the transcription pattern of the above genes was consistent with the transcriptome. The differences in the transcript levels of the above genes may be the potential reason for the strong tolerance of soybean hairy roots overexpressing the GsEXLB14 gene under salt and drought stress. In conclusion, the expansin GsEXLB14 can be used as a valuable candidate gene for the molecular breeding of soybeans.

Transcriptome analysis and functional verification reveal the roles of copper in resistance to potato virus Y infection in tobacco

Potato virus Y (PVY) is one of the most important pathogens in the genus Potyvirus that seriously harms agricultural production. Copper (Cu), as a micronutrient, is closely related to plant immune response. In this study, we found that foliar application of Cu could inhibit PVY infection to some extent, especially at 7 days post inoculation (dpi). To explore the effect of Cu on PVY infection, transcriptome sequencing analysis was performed on PVY-infected tobacco with or without Cu application. Several key pathways regulated by Cu were identified, including plant-pathogen interaction, inorganic ion transport and metabolism, and photosynthesis. Moreover, the results of virus-induced gene silencing (VIGS) assays revealed that NbMLP423, NbPIP2, NbFd and NbEXPA played positive roles in resistance to PVY infection in Nicotiana benthamiana. In addition, transgenic tobacco plants overexpressing NtEXPA11 showed increased resistance to PVY infection. These results contribute to clarify the role and regulatory mechanism of Cu against PVY infection, and provide candidate genes for disease resistance breeding.

An ex vitro hairy root system from petioles of detached soybean leaves for in planta screening of target genes and CRISPR strategies associated with nematode bioassays

MAIN CONCLUSION

The ex vitro hairy root system from petioles of detached soybean leaves allows the functional validation of genes using classical transgenesis and CRISPR strategies (e.g., sgRNA validation, gene activation) associated with nematode bioassays. Agrobacterium rhizogenes-mediated root transformation has been widely used in soybean for the functional validation of target genes in classical transgenesis and single-guide RNA (sgRNA) in CRISPR-based technologies. Initial data showed that in vitro hairy root induction from soybean cotyledons and hypocotyls were not the most suitable strategies for simultaneous performing genetic studies and nematode bioassays. Therefore, an ex vitro hairy root system was developed for in planta screening of target molecules during soybean parasitism by root-knot nematodes (RKNs). Applying this method, hairy roots were successfully induced by A. rhizogenes from petioles of detached soybean leaves. The soybean GmPR10 and GmGST genes were then constitutively overexpressed in both soybean hairy roots and tobacco plants, showing a reduction in the number of Meloidogyne incognita-induced galls of up to 41% and 39%, respectively. In addition, this system was evaluated for upregulation of the endogenous GmExpA and GmExpLB genes by CRISPR/dCas9, showing high levels of gene activation and reductions in gall number of up to 58.7% and 67.4%, respectively. Furthermore, morphological and histological analyses of the galls were successfully performed. These collective data validate the ex vitro hairy root system for screening target genes, using classical overexpression and CRISPR approaches, directly in soybean in a simple manner and associated with nematode bioassays. This system can also be used in other root pathosystems for analyses of gene function and studies of parasite interactions with plants, as well as for other purposes such as studies of root biology and promoter characterization.