Physiological and Proteomic Responses of Contrasting Alfalfa (Medicago sativa L.) Varieties to High Temperature Stress

Tandem mass tag (TMT)-based quantitative proteomics analysis reveals the different responses of contrasting alfalfa varieties to drought stress

BACKGROUND

Drought stress restricts the growth, distribution and productivity of alfalfa (Medicago sativa L.). In order to study the response differences of alfalfa cultivars to drought stress, we previously carried out physiological and molecular comparative analysis on two alfalfa varieties with contrasting drought resistance (relatively drought-tolerant Longdong and drought-sensitive Algonquin). However, the differences in proteomic factors of the two varieties in response to drought stress still need to be further studied. Therefore, TMT-based quantitative proteomic analysis was performed using leaf tissues of the two alfalfa cultivars to identify and uncover differentially abundant proteins (DAPs).

RESULTS

In total, 677 DAPs were identified in Algonquin and 277 in Longdong under drought stress. Subsequently, we conducted various bioinformatics analysis on these DAPs, including subcellular location, functional classification and biological pathway enrichment. The first two main COG functional categories of DAPs in both alfalfa varieties after drought stress were 'Translation, ribosomal structure and biogenesis' and 'Posttranslational modification, protein turnover, chaperones'. According to KEGG database, the DAPs of the two alfalfa cultivars after drought treatment were differentially enriched in different biological pathways. The DAPs from Algonquin were enriched in 'photosynthesis' and 'ribosome'. The pathways of 'linoleic acid metabolism', 'protein processing in endoplasmic reticulum' and 'RNA transport' in Longdong were significantly enriched. Finally, we found significant differences in DAP enrichment and expression patterns between Longdong and Algonquin in glycolysis/glycogenesis, TCA cycle, photosynthesis, protein biosynthesis, flavonoid and isoflavonoid biosynthesis, and plant-pathogen interaction pathway after drought treatment.

CONCLUSIONS

The differences of DAPs involved in various metabolic pathways may explain the differences in the resistance of the two varieties to drought stress. These DAPs can be used as candidate proteins for molecular breeding of alfalfa to cultivate new germplasm with more drought tolerance to adapt to unfavorable environments.

Analysis of Photosynthetic Characteristics and Screening High Light-Efficiency Germplasm in Sugarcane

Sugarcane is a globally significant crop for sugar and energy production, and developing high light-efficiency sugarcane varieties is crucial for enhancing yield and quality. However, limited research is available on the screening of sugarcane germplasm with high photosynthetic efficiency, especially with different leaf positions. The present study, conducted in Guangxi, China, aimed to analyze the photosynthetic characteristics of 258 sugarcane varieties at different leaf positions over three consecutive years in field experiments. The results showed significant differences in photosynthetic characteristics among genotypes, years, and leaf positions. Heritability estimates for various photosynthetic parameters ranged from 0.76 to 0.88. Principal component analysis revealed that the first three principal components accounted for over 99% of the cumulative variance. The first component represented photosynthetic efficiency and light utilization, the second focused on electron transfer and reaction center status, and the third was associated with chlorophyll content. Cluster and discriminant analysis classified sugarcane genotypes into three categories: high photosynthetic efficiency (HPE) with 86 genotypes, medium photosynthetic efficiency (MPE) with 60 genotypes, and low photosynthetic efficiency (LPE) with 112 genotypes. Multi-year trials confirmed that HPE sugarcane genotypes had higher single-stem weight and sucrose content. This study provides valuable insights into the photosynthetic physiological characteristics of different sugarcane varieties, which can contribute to further research regarding high yields and sugar breeding.

Proteomic and physiological responses of contrasting two different heat-resistant orchardgrass genotypes to heat stress

As an important forage crop worldwide, the growth and productivity of orchardgrass are greatly impacted by high temperatures. However, little information is known about how orchardgrass proteomic changes under heat conditions. Therefore, the present study investigated the proteomics and physiological changes in 667 [AKZ-NRGR667 (heat-tolerant)] and 7602 [PI237602 (heat-sensitive)] under heat stress (40/35 °C). In addition, the responses of translational regulating of heat stress in orchardgrass were analyzed through proteomic changes using the tandem mass tags (TMT) technique. Together, 410 differentially expressed proteins (DEPs) were identified from two orchardgrass genotypes under heat at 24 h. Proteomics analyses indicated that proteins related to substance metabolism, photosynthesis, and heat shock proteins (HSPs) were differentially expressed under heat stress and control conditions. Moreover, a large proportion of HSPs were expressed in the heat-tolerant genotype as compared to the heat-sensitive genotype. In conclusion, genotype 667 has higher adaptability and repairing capability due to stronger heat tolerance capacity that can make it more suited to sustaining its survival and growth than genotype 7602. These findings can provide the basis for genetic improvements in orchardgrass and other crops facing high-temperature stress or heat environment that may lead to heat resistance or tolerance.

Identification of genetic and biochemical mechanisms associated with heat shock and heat stress adaptation in grain amaranths

Heat stress is poised to become a major factor negatively affecting plant performance worldwide. In terms of world food security, increased ambient temperatures are poised to reduce yields in cereals and other economically important crops. Grain amaranths are known to be productive under poor and/or unfavorable growing conditions that significantly affect cereals and other crops. Several physiological and biochemical attributes have been recognized to contribute to this favorable property, including a high water-use efficiency and the activation of a carbon starvation response. This study reports the behavior of the three grain amaranth species to two different stress conditions: short-term exposure to heat shock (HS) conditions using young plants kept in a conditioned growth chamber or long-term cultivation under severe heat stress in greenhouse conditions. The latter involved exposing grain amaranth plants to daylight temperatures that hovered around 50°C, or above, for at least 4 h during the day and to higher than normal nocturnal temperatures for a complete growth cycle in the summer of 2022 in central Mexico. All grain amaranth species showed a high tolerance to HS, demonstrated by a high percentage of recovery after their return to optimal growing conditions. The tolerance observed coincided with increased expression levels of unknown function genes previously shown to be induced by other (a)biotic stress conditions. Included among them were genes coding for RNA-binding and RNA-editing proteins, respectively. HS tolerance was also in accordance with favorable changes in several biochemical parameters usually induced in plants in response to abiotic stresses. Conversely, exposure to a prolonged severe heat stress seriously affected the vegetative and reproductive development of all three grain amaranth species, which yielded little or no seed. The latter data suggested that the usually stress-tolerant grain amaranths are unable to overcome severe heat stress-related damage leading to reproductive failure.

Effect of arbuscular mycorrhizal fungi (Glomus mosseae) and elevated air temperature on Cd migration in the rhizosphere soil of alfalfa

Cadmium (Cd) migration in the rhizosphere soil is easily affected by plants and microorganisms. Global warming significantly affects plant growth, and arbuscular mycorrhizal fungi (AMF) can chelate heavy metals by mycelium, cell wall components, and mycelial secretion. Here, we investigated the regulation of Glomus mosseae on Cd migration in the rhizosphere soil of alfalfa under elevated temperature (ET, + 3 °C). Elevated temperature significantly decreased G. mosseae colonization rate in the roots by 49.5% under Cd exposure. Under ET + G. mosseae + Cd relative to ET + Cd, the contents of free amino acids, total and easily extractable glomalin-related soil protein (GRSP), and root Cd increased significantly; however, the changes in DTPA-Cd in the rhizosphere soil and Cd in the shoots were insignificant. In addition, G. mosseae colonization enhanced the bioconcentration factor of Cd in the roots and the total removal rate of Cd in the rhizosphere soil by 63.4% and 16.3%, respectively, under ET + Cd. However, the changes in the expression of iron-regulated transport 1 (IRT1) and natural resistance-associated macrophage protein 1 genes were insignificant under ET + G. mosseae + Cd relative to ET + Cd. In summary, temperature and G. mosseae significantly affected Cd fate in the rhizosphere soil, and IRT1 gene and rhizosphere soil pH, N, and C/N ratio were significant factors influencing Cd migration. Additionally, G. mosseae improved the remediation efficiency of Cd-contaminated soils by alfalfa under ET. The results will help us understand the regulation of AMF on the phytoremediation of heavy metal-contaminated soils under global warming scenarios.