A LEA gene regulates Cadmium tolerance by mediating physiological responses

Physiological and transcriptional mechanisms associated with cadmium stress tolerance in Hibiscus syriacus L

BACKGROUND

Cadmium (Cd) pollution of soils is a global concern because its accumulation in plants generates severe growth retardation and health problems. Hibiscus syriacus is an ornamental plant that can tolerate various abiotic stresses, including Cd stress. Therefore, it is proposed as a plant material in Cd-polluted areas. However, the molecular mechanisms of H. syriacus tolerance to Cd are not yet understood.

RESULTS

This study investigated the physiological and transcriptional response of "Hongxing", a Cd²⁺-tolerant H. syriacus variety, grown on a substrate containing higher concentration of Cd (400 mg/kg). The Cd treatment induced only 28% of plant mortality, but a significant decrease in the chlorophyll content was observed. Malondialdehyde content and activity of the antioxidant enzymes catalase, peroxidase, and superoxide dismutase were significantly increased under Cd stress. Transcriptome analysis identified 29,921 differentially expressed genes (DEGs), including 16,729 down-regulated and 13,192 up-regulated genes, under Cd stress. Functional enrichment analyses assigned the DEGs mainly to plant hormone signal transduction, transport, nucleosome and DNA processes, mitogen-activated protein kinase signaling pathway, antioxidant process, fatty acid metabolism, and biosynthesis of secondary metabolites. Many MYB, EP2/ERF, NAC, WRKY family genes, and genes containing metal binding domains were up-regulated, implying that they are essential for the Cd-stress response in H. syriacus. The most induced genes were filtered out, providing valuable resources for future studies.

CONCLUSIONS

Our findings provide insights into the molecular responses to Cd stress in H. syriacus. Moreover, this study offers comprehensive and important resources for future studies toward improving the plant Cd tolerance and its valorization in phytoremediation.

Nitrogen sources affected the biosynthesis of 2-acetyl-1-pyrroline, cooked rice elongation and amylose content in rice

Many studies have been carried out on N sources effect on fragrant rice; however, their impact on rice grain quality is largely unclear. In this study, we evaluated the effects of different types of N sources on rice growth, yield, 2-acetyl-1-pyrroline (2AP), amylose and cooked rice elongation. Two indica rice cultivars, Basmati 385 (B385), Xiangyaxiangzhan (XYXZ) and two japonica cultivars, Yunjingyou (YJY), Daohuaxiang (DHX) were grown in experimental pots with six replications under four N sources: Potassium nitrate (KNO3), ammonium bicarbonate (NH4HCO3), urea (H2NCONH2) and sodium nitrate (NaNO3) in 2019 and 2020 early seasons. Our results showed that N dynamics regulated the number of panicles, 1000-grain weight, grain yield, 2-acetyl-1-pyrroline, amylose and cooked rice elongation across all the four treatments. The NH4HCO3 treatment significantly increased the number of panicles and grain yield across the four rice varieties compared with KNO3, H2NCONH2 and NaNO3 N sources in both 2019 and 2020 early season, The KNO3 treatment significantly showed higher 1000-grain weight in B-385, YJY, XYXZ and DHX compared to other N sources. Compared with other N sources treatment, the NH4HCO3 treatments significantly increased the 2AP contents in heading stage leaves, matured leaves and grains of B-385, YJY, XYXZ and DHX respectively. Cooked rice elongation percentage also showed significant difference in all treatments studied with KNO3 recorded the highest across the four varieties. Analysis of major enzymes and compounds such as P5C, P5CS, PDH, Pyrroline, proline and Methylglyoxal showed remarkable differences in each cultivar at heading and maturity stages with higher activity in NH4HCO3 and H2NCONH2 treatments. Similarly, in all treatments, we also observed significant increase in amylose content percentage, with NH4HCO3 having greater percentage of amylose.

Physiological and biochemical analysis of mechanisms underlying cadmium tolerance and accumulation in turnip

The capacity of plants to accumulate cadmium (Cd) is significant for phytoremediation of Cd-polluted soils. Turnips cultivated in China include species featuring high Cd accumulation and some of these plants act as Cd hyperaccumulator landraces. These plants can accumulate over 100 mg Cd kg-1 dry weight in leaves without injury. Hence, studies that explore mechanisms underlying Cd detoxification and transport in turnip plants are essential. In the present study, we compared physiological and biochemical changes in turnip leaves treated with two Cd concentrations to controls. We discovered that Cd stress significantly increased the enzymatic activities or compound contents in the antioxidant system, including members of the glutathione-ascorbic acid cycle, whereas oxidation of reactive oxygen species (ROS) remained stable. Cd treatments also increased the contents of phytochelatins as well as a number of amino acids. Based on these results, we conclude that turnips initiate a series of response processes to manage Cd treatment. First, the antioxidant system maintaining ROS homeostasis and osmotic adjustment is excited to maintain stability of cell osmotic potential. Cd is chelated into its stable form to reduce its toxicity. Cd is possibly transported to vacuoles or non-protoplasts for isolation. Amino acid synthesis may directly and indirectly play an important role in these processes. This study partly revealed physiological and biochemical mechanisms underlying turnip response to Cd stress and provides information on artificially increasing or decreasing Cd accumulation in turnips and other plants.

Co-transforming bar and CsLEA enhanced tolerance to drought and salt stress in transgenic alfalfa (Medicago sativa L.)

Drought and high salinity are two major abiotic factors that restrict alfalfa productivity. A dehydrin protein, CsLEA, from the desert grass Cleistogenes songorica was transformed into alfalfa (Medicago sativa L.) via Agrobacterium-mediated transformation using the bar gene as a selectable marker, and the drought and salt stress tolerances of the transgenic plants were assessed. Thirty-nine of 119 transformants were positive, as screened by Basta, and further molecularly authenticated using PCR and RT-PCR. Phenotype observations revealed that the transgenic plants grew better than the wild-type (WT) plants after 15d of drought stress and 10d of salt stress: the leaves of WT alfalfa turned yellow, whereas the transgenic alfalfa leaves only wilted; after rewatering, the transgenic plants returned to a normal state, though the WT plants could not be restored. Evaluation of physiologic and biochemical indices during drought and salt stresses showed a relatively lower Na(+) content in the leaves of the transgenic plants, which would reduce toxic ion effects. In addition, the transgenic plants were able to maintain a higher relative water content (RWC), higher shoot biomass, fewer photosystem changes, decreased membrane injury, and a lower level of osmotic stress injury. These results demonstrate that overexpression of the CsLEA gene can enhance the drought and salt tolerance of transgenic alfalfa; in addition, carrying the bar gene in the genome may increase herbicide resistance.

Comparative transcriptional profiling of two wheat genotypes, with contrasting levels of minerals in grains, shows expression differences during grain filling

Wheat is one of the most important cereal crops in the world. To identify the candidate genes for mineral accumulation, it is important to examine differential transcriptome between wheat genotypes, with contrasting levels of minerals in grains. A transcriptional comparison of developing grains was carried out between two wheat genotypes- Triticum aestivum Cv. WL711 (low grain mineral), and T. aestivum L. IITR26 (high grain mineral), using Affymetrix GeneChip Wheat Genome Array. The study identified a total of 580 probe sets as differentially expressed (with log2 fold change of ≥2 at p≤0.01) between the two genotypes, during grain filling. Transcripts with significant differences in induction or repression between the two genotypes included genes related to metal homeostasis, metal tolerance, lignin and flavonoid biosynthesis, amino acid and protein transport, vacuolar-sorting receptor, aquaporins, and stress responses. Meta-analysis revealed spatial and temporal signatures of a majority of the differentially regulated transcripts.