The SbbHLH041–SbEXPA11 Module Enhances Cadmium Accumulation and Rescues Biomass by Increasing Photosynthetic Efficiency in Sorghum

Abstract

In plants, expansin genes are responsive to heavy metal exposure. To study the bioremediary potential of this important gene family, we discovered a root-expressed expansin gene in sorghum, SbEXPA11, which is notably upregulated following cadmium (Cd) exposure. However, the mechanism underlying the Cd detoxification and accumulation mediated by SbEXPA11 in sorghum remains unclear. We overexpressed SbEXPA11 in sorghum and compared wild-type (WT) and SbEXPA11-overexpressing transgenic sorghum in terms of Cd accumulation and physiological indices following Cd. Compared with the WT, we found that SbEXPA11 mediates Cd tolerance by exerting reactive oxygen species (ROS)-scavenging effects through upregulating the expression of antioxidant enzymes. Moreover, the overexpression of SbEXPA11 rescued biomass production by increasing the photosynthetic efficiency of transgenic plants. In the pot experiment with a dosage of 10 mg/kg Cd, transgenic sorghum plants demonstrated higher efficacy in reducing the Cd content of the soil (8.62 mg/kg) compared to WT sorghum plants (9.51 mg/kg). Subsequent analysis revealed that the SbbHLH041 transcription factor has the ability to induce SbEXPA11 expression through interacting with the E-box located within the SbEXPA11 promoter. These findings suggest that the SbbHLH041–SbEXPA11 cascade module may be beneficial for the development of phytoremediary sorghum varieties.

Abiotic Stress Tolerance Boosted by Genetic Diversity in Plants

“…Finally, downstream greenhouse-based validation of the rescued variants for adaptation to abiotic stresses is carried out with expression analysis and transgenesis. SbEXPA11 is a target to develop phytoremediary sorghum varieties Wang et al [37] The table is sorted top-down by scope and species. The scope is classified as follows: • molecular in silico characterization, + genetic mapping, ‡ gene functional validation with expression analysis, and § trans-genesis for gene functional validation.…”

“…Last but not least, Wang et al [37] also studied toxicity in sorghum, this time for cadmium (Cd), yet went a step further in terms of the candidate gene validation path by recurring to trans-genesis for functional corroboration. Specifically, the team overexpressed SbEXPA11 to validate its functionality during Cd exposure as a target for phytoremediation.…”

“…Specifically, the team overexpressed SbEXPA11 to validate its functionality during Cd exposure as a target for phytoremediation. This potential application is highly feasible, at least as proof of concept, because through examining the expansin gene family's reaction to heavy metal exposure, Wang et al [37] corroborated that SbEXPA11 possesses the capacity to accumulate and detoxify Cd. These researchers further clarified how SbEXPA11 conveys Cd tolerance by scavenging reactive oxygen species (ROS), and increasing the production of antioxidant enzymes.…”

“…Data Availability Statement: For data availability, please see the original articles [31][32][33][34][35][36][37] within the Special Issue "Abiotic Stress Tolerance and Genetic Diversity in Plants" (https://www.mdpi.com/ journal/ijms/special_issues/80P9M9NK87 accessed on 24 March 2023).…”