Differential Morpho-Physiological and Transcriptomic Responses to Heat Stress in Two Blueberry Species

Pyramiding of transcription factor, PgHSF4, and stress-responsive genes of p68, Pg47, and PsAKR1 impart multiple abiotic stress tolerance in rice (Oryza sativa L.)

Abiotic stresses such as drought, salinity, and heat stress significantly affect rice crop growth and production. Under uncertain climatic conditions, the concurrent multiple abiotic stresses at different stages of rice production became a major challenge for agriculture. Hence, improving rice's multiple abiotic stress tolerance is essential to overcome unprecedented challenges under adverse environmental conditions. A significant challenge for rice breeding programs in improving abiotic stress tolerance involves multiple traits and their complexity. Multiple traits must be targeted to improve multiple stress tolerance in rice and uncover the mechanisms. With this hypothesis, in the present study gene stacking approach is used to integrate multiple traits involved in stress tolerance. The multigene transgenics co-expressing Pennisetum glaucum 47 (Pg47), Pea 68 (p68), Pennisetum glaucum Heat Shock Factor 4(PgHSF4), and Pseudomonas Aldo Keto Reductase 1 (PsAKR1) genes in the rice genotype (AC39020) were developed using the in-planta transformation method. The promising transgenic lines maintained higher yields under semi-irrigated aerobic cultivation (moisture stress). These 15 promising transgenic rice seedlings showed improved shoot and root growth traits under salinity, accelerating aging, temperature, and oxidative stress. They showed better physiological characteristics, such as chlorophyll content, membrane stability, and lower accumulation of reactive oxygen species, under multiple abiotic stresses than wild-type. Enhanced expression of transgenes and other stress-responsive downstream genes such as HSP70, SOD, APX, SOS, PP2C, and P5CS in transgenic lines suggest the possible molecular mechanism for imparting the abiotic stress tolerance. This study proved that multiple genes stacking as a novel strategy induce several mechanisms and responsible traits to overcome multiple abiotic stresses. This multigene combination can potentially improve tolerance to multiple abiotic stress conditions and pave the way for developing climate-resilient crops.

Genomic and evolutionary relationships among wild and cultivated blueberry species

BACKGROUND

Blueberries (Vaccinium section Cyanococcus) are an economically important fruit crop in the United States. Understanding genetic structure and relationships in blueberries is essential to advance the genetic improvement of horticulturally important traits. In the present study, we investigated the genomic and evolutionary relationships in 195 blueberry accessions from five species (comprising 33 V. corymbosum, 14 V. boreale, 81 V. darrowii, 29 V. myrsinites, and 38 V. tenellum) using single nucleotide polymorphisms (SNPs) mined from genotyping-by-sequencing (GBS) data.

RESULTS

GBS generated ~ 751 million raw reads, of which 79.7% were mapped to the reference genome V. corymbosum cv. Draper v1.0. After filtering (read depth > 3, minor allele frequency > 0.05, and call rate > 0.9), 60,518 SNPs were identified and used in further analyses. The 195 blueberry accessions formed three major clusters on the principal component (PC) analysis plot, in which the first two PCs accounted for 29.2% of the total genetic variance. Nucleotide diversity (π) was highest for V. tenellum and V. boreale (0.023 each), and lowest for V. darrowii (0.012). Using TreeMix analysis, we identified four migration events and deciphered gene flow among the selected species. In addition, we detected a strong V. boreale lineage in cultivated blueberry species. Pairwise SweeD analysis identified a wide sweep (encompassing 32 genes) as a strong signature of domestication on the scaffold VaccDscaff 12. From this region, five genes encoded topoisomerases, six genes encoded CAP-gly domain linker (which regulates the dynamics of the microtubule cytoskeleton), and three genes coded for GSL8 (involved in the synthesis of the cell wall component callose). One of the genes, augustus_masked-VaccDscaff12-processed-gene-172.10, is a homolog of Arabidopsis AT2G25010 and encodes the protein MAINTENANCE OF MERISTEMS-like involved in root and shoot growth. Additional genomic stratification by admixture analysis identified genetic lineages and species boundaries in blueberry accessions. The results from this study indicate that V. boreale is a genetically distant outgroup, while V. darrowii, V. myrsinites, and V. tenellum are closely related.

CONCLUSION

Our study provides new insights into the evolution and genetic architecture of cultivated blueberries.

Transcriptome profiling, physiological, and biochemical analyses provide new insights towards drought stress response in sugar maple (Acer saccharum Marshall) saplings

Sugar maple (Acer saccharum Marshall) is a temperate tree species in the northeastern parts of the United States and is economically important for its hardwood and syrup production. Sugar maple trees are highly vulnerable to changing climatic conditions, especially drought, so understanding the physiological, biochemical, and molecular responses is critical. The sugar maple saplings were subjected to drought stress for 7, 14, and 21 days and physiological data collected at 7, 14, and 21 days after stress (DAS) showed significantly reduced chlorophyll and Normalized Difference Vegetation Index with increasing drought stress time. The drought stress-induced biochemical changes revealed a higher accumulation of malondialdehyde, proline, and peroxidase activity in response to drought stress. Transcriptome analysis identified a total of 14,099 differentially expressed genes (DEGs); 328 were common among all stress periods. Among the DEGs, transcription factors (including NAC, HSF, ZFPs, GRFs, and ERF), chloroplast-related and stress-responsive genes such as peroxidases, membrane transporters, kinases, and protein detoxifiers were predominant. GO enrichment and KEGG pathway analysis revealed significantly enriched processes related to protein phosphorylation, transmembrane transport, nucleic acids, and metabolic, secondary metabolite biosynthesis pathways, circadian rhythm-plant, and carotenoid biosynthesis in response to drought stress. Time-series transcriptomic analysis revealed changes in gene regulation patterns in eight different clusters, and pathway analysis by individual clusters revealed a hub of stress-responsive pathways. In addition, qRT-PCR validation of selected DEGs revealed that the expression patterns were consistent with transcriptome analysis. The results from this study provide insights into the dynamics of physiological, biochemical, and gene responses to progressive drought stress and reveal the important stress-adaptive mechanisms of sugar maple saplings in response to drought stress.

Leaf water potential-dependent leaflet closure contributes to legume leaves cool down and drought avoidance under diurnal drought stress

Efficient thermoregulation under diurnal drought stress protects leaves from photosystem damage and water supply-demand imbalance, yet the cool effect and drought avoidance by leaflet closure have not been well understood. We investigated the cool effect and the drought avoidance of leaflet closure in legume species that survived in the semi-arid region facing seasonal and diurnal drought stress. The results showed that leaflet closure effectively cooled down legume leaves through a reduction of projected leaflet area and the cosine of the angle of incidence (cos i). The leaflet closure was strongly dependent on leaf water potential (Ψleaf). In addition, by characterizing the sequence of key leaf drought response traits, we found leaflet closure occurred after stomatal closure and reduced transpiration rate but before hydraulic failure and turgor loss point (Ψtlp). The meta-analysis also showed that the leaflet closure and cos i decreased after the stomatal conductance declined but before midday. These results imply that Ψleaf-dependent leaflet closure as an alternative to transpiration for leaflet cooling down and as a protective drought avoidance strategy assisting sessile legume plants survival under drought stress.

Comparative Physiological and Transcriptomic Analyses of Improved Heat Stress Tolerance in Celery (Apium Graveolens L.) Caused by Exogenous Melatonin

Melatonin (MT) is crucial in plant growth, development, and response to stress. Celery is a vegetable that grows in a cool climate, and a hot climate can deteriorate its growth, yield, and quality. This study investigates the effect of exogenous melatonin on celery physiology. Transcriptional levels were analyzed by spraying celery with exogenous MT before exposing it to high temperatures. The regulatory mechanism of exogenous MT-mediated heat tolerance was examined. The results show that the exogenous MT reduced the thermal damage state of celery seedlings, as well as the malondialdehyde (MDA) content and relative conductivity (REC), increasing the oxidase activity, the osmotic regulatory substances, and chlorophyll, enhancing the leaf transpiration and the light energy utilization efficiency. We examined the mechanism of exogenous MT in mitigating high-temperature damage using the transcriptome sequencing method. A total of 134 genes were expressed differently at high temperature in the celery treated with MT compared with the untreated celery. Functional annotation analysis revealed that the differentially expressed genes were abundant in the “pyruvate metabolism” pathway and the “peroxidase activity” pathway. According to the pathway-based gene expression analysis, exogenous MT can inhibit the upregulation of pyruvate synthesis genes and the downregulation of pyruvate consumption genes, preventing the accumulated pyruvate from rapidly upregulating the expression of peroxidase genes, and thereby enhancing peroxidase activity. RT-qPCR verification showed a rising encoding peroxidase gene expression under MT treatment. The gene expression pattern involved in pyruvate anabolism and metabolism agreed with the abundant transcriptome expression, validating the physiological index results. These results indicate that the application of exogenous MT to celery significantly enhances the ability of plant to remove reactive oxygen species (ROS) in response to heat stress, thereby improving the ability of plant to resist heat stress. The results of this study provide a theoretical basis for the use of MT to alleviate the damage caused by heat stress in plant growth and development.