Transgenic Medicago truncatula Plants That Accumulate Proline Display Enhanced Tolerance to Cadmium Stress

Abstract

Cadmium (Cd) accumulation in agricultural soils constitutes a serious problem for crop yields and food safety. It is known that proline (Pro) can rapidly accumulate in plant tissues in response to abiotic stress. To analyze the potential protective effect of Pro accumulation against Cd toxicity, we compared the response to Cd stress of wild-type (WT) Medicago truncatula and a transgenic line that we had previously obtained and characterized (p18), which expressed the Δ1-pyrroline-5-carboxylate synthetase gene from Vigna aconitifolia (VaP5CS), and accumulated high Pro levels. Cadmium significantly reduced germination of WT seeds compared to p18 seeds, and seedling relative root growth, a valid indicator of metal tolerance, was significantly higher for p18 than WT seedlings. We analyzed the relative expression of genes related to Pro metabolism, phytochelatin biosynthesis. antioxidant machinery, and NADPH recycling, which are relevant mechanisms in the response to Cd stress. They presented differential expression in the seedlings of both genotypes both under control conditions and under Cd stress, suggesting that the Cd response mechanisms might be constitutively activated in the transgenic line. Pro accumulation promoted higher survival, enhanced growth performance, and minor nutrient imbalance in transgenic p18 plants compared to WT plants. These facts, together with the recorded gluthatione levels, lipid peroxidation and antioxidant enzyme activities strongly suggested that VaP5CS expression and Pro accumulation conferred enhanced Cd tolerance to M. truncatula p18 plants, which was likely mediated by changes in Pro metabolism, increased phytochelatin biosynthesis and a more efficient antioxidant response. Moreover, p18 roots accumulated significantly higher Cd amounts than WT roots, while Cd translocation to the aerial part was similar to WT plants, thus suggesting that high Pro levels increased not only Cd tolerance, but also Cd phytostabilization by rhizosequestration.

Effects of Inoculation with Stress-Tolerant Rhizobia on the Response of Alfalfa (Medicago sativa L.) to Combined Salinity and Cadmium Stress

“…Rhizobial inoculation has been previously described to promote proline accumulation under cadmium [73] or salt stress [50]. This is in agreement with previous studies by our group that show that transgenic M. truncatula plants that accumulate proline are more tolerant to salt and Cd stress [23,74]. MsProDH expression was higher in inoculated than in fertilized plants.…”

“…The primary defense against ROS includes superoxide dismutase (SOD) enzymes that catalyze the dismutation of O 2 − (superoxide) to O 2 and H 2 O 2. Then, catalases and peroxidases detoxify H 2 O 2 [23].…”

Response mechanisms of sugarcane seedlings to the allelopathic effects of root aqueous extracts from sugarcane ratoons of different ages

“…These results are consistent with those reported by Gao et al (2009) who showed that salt stress can significantly increase the Pro content in plants. Thus, stress can promote the natural responses of plant tissues to induce the transformation and accumulation of a large amount of Pro ( García de la Torre et al., 2022 ), thereby improving the osmoregulatory and stress alleviation abilities of plant tissues under adverse conditions and assisting in the maintenance of normal plant metabolism.…”

Cadmium toxicity in medicinal plants: An overview of the tolerance strategies, biotechnological and omics approaches to alleviate metal stress

“…Transgenic Medicago truncatula expressing Delta(1)-pyrroline-5-carboxylate synthetase (P5CS) has been established by Verdoy et al (2006) by infecting the host plant with Agrobacterium rhizogenes EHA105 carrying VaP5CS from Vigna aconitifolia. The VaP5CS gene in transgenic Medicago truncatula has been reported as being involved in conferring cadmium tolerance by enhanced proline accumulation and antioxidant activity by Garcıá de la Torre et al, (2022). Very limited attempts at genetic engineering in medicinal plants have been reported till date.…”

“…In Catharanthus roseus , the expression of terpenoid indole alkaloid (TIA) genes like STR, DAT, SGD, SLS, PRS, TDC, MTs, TPT, and MDR has been triggered under Cd toxicity ( Chen et al., 2018c ). In the comparative study of Cd-sensitive and Cd-tolerant Medicago truncatula , it was found that the overexpression of GSH and phytochelatin biosynthesis genes such as MtCYS, MtγECS, MtGSHS, MtGR, and MtG6PDH in Cd sensitive plant ( García de la Torre et al., 2022 ). While the enhanced expression of metallothionein genes from the families MT1, MT2 and MT3 in response to Cd stress in Phytolacca americana was reported by Chen et al.…”