Genetic improvement through overexpressing PuP5CS in switchgrass is feasible for enhancing plant salt stress tolerance. Switchgrass (Panicum virgatum L.) has developed into a dedicated bioenergy crop. To improve the biomass production of switchgrass grown on different types of soil, abiotic stress tolerance traits are considered for its genetic improvement. Proline accumulation is a widespread response when plants are subjected to abiotic stresses such as drought, cold and salinity. In plants, P5CS gene encodes the key regulatory enzyme that plays a crucial role in proline biosynthesis. Here, we introduced the PuP5CS gene (from Puccinellia chinampoensis) into switchgrass by Agrobacterium-mediated transformation. Transgenic lines overexpressing the PuP5CS gene showed phenotypic advantages, in leaf width, internode diameter, internode length, tiller numbers and precocious flowering under normal conditions, and the transgenic lines displayed better regenerative capacity in forming more tillers after harvest. Moreover, the PuP5CS gene enhanced the salt tolerance of transgenic switchgrass by altering a wide range of physiological responses. In accordance with the physiological results, histological analysis of cross sections through the leaf blade showed that the areas of bulliform cells and bundle sheath cells were significantly increased in PuP5CS-overexpressing leaves. The expression levels of ROS scavenging-associated genes in transgenic plants were higher than in control plants under salt stress. The results show that genetic improvement through overexpressing PuP5CS in switchgrass is feasible for enhancing plant stress tolerance.

Background High temperature seriously limits the annual production of fresh cut lilies, which is one of the four major cut flowers in the global cut flower market. There were few transcriptomes focused on the gene expression of lilies under heat stress. In order to reveal the potential heat response patterns in bulbous plants and provide important genes for further genetic engineering techniques to improve thermotolerance of lily, RNA sequencing of lilies under heat treatments were conducted. Results In this study, seedlings of Lilium longiflorum ‘White Heaven’ were heat-treated at 37 °C for different lengths of time (0 h, 0.5 h, 1 h, 3 h, 6 h, and 12 h with a 12 h-light/12 h-dark cycle). The leaves of these lily seedlings were immediately collected after heat treatments and quickly put into liquid nitrogen for RNA sequencing. 109,364,486–171,487,430 clean reads and 55,044 unigenes including 21,608 differentially expressed genes (DEGs) (fold change ≥2) were obtained after heat treatment. The number of DEGs increased sharply during the heat treatments of 0.5 h–1 h and 1 h–3 h compared to that of other periods. Genes of the heat stress transcription factor (HSF) family and the small heat shock proteins (small HSPs, also known as HSP20) family responded to heat stress early and quickly. Compared to that of the calcium signal and hormone pathways, DEGs of the HSF-HSP pathway and reactive oxygen species (ROS) pathway were significantly and highly induced. Moreover, they had the similar expression pattern in response to heat stress. Small HSPs family genes were the major components in the 50 most highly induced genes at each heat stress treatment and involved in ROS pathway in the rapid response to heat stress. Furthermore, the barley stripe mosaic virus induced gene silencing (BSMV-VIGS) of LlHsfA2 caused a significantly reduced thermotolerance phenotype in Lilium longiflorum ‘White Heaven’, meanwhile decreasing the expression of small HSPs family genes and increasing the ROS scavenging enzyme ascorbate peroxidase (APX) genes, indicating the potential interplay between these two pathways. Conclusions Based on our transcriptomic analysis, we provide a new finding that small HSPs play important roles in crosstalk between HSF-HSP and ROS pathways in heat stress response of lily, which also supply the groundwork for understanding the mechanism of heat stress in bulbous plants.

Heat stress severely affects the annual agricultural production. Heat stress transcription factors (HSFs) represent a critical regulatory juncture in the heat stress response (HSR) of plants. The HsfA1-dependent pathway has been explored well, but the regulatory mechanism of the HsfA1-independent pathway is still under-investigated. In the present research, HsfA4, an important gene of the HsfA1-independent pathway, was isolated from lilies (Lilium longiflorum) using the RACE method, which encodes 435 amino acids. LlHsfA4 contains a typical domain of HSFs and belongs to the HSF A4 family, according to homology comparisons and phylogenetic analysis. LlHsfA4 was mainly expressed in leaves and was induced by heat stress and H2O2 using qRT-PCR and GUS staining in transgenic Arabidopsis. LlHsfA4 had transactivation activity and was located in the nucleus and cytoplasm through a yeast one hybrid system and through transient expression in lily protoplasts. Over expressing LlHsfA4 in Arabidopsis enhanced its basic thermotolerance, but acquired thermotolerance was not achieved. Further research found that heat stress could increase H2O2 content in lily leaves and reduced H2O2 accumulation in transgenic plants, which was consistent with the up-regulation of HSR downstream genes such as Heat stress proteins (HSPs), Galactinol synthase1 (GolS1), WRKY DNA binding protein 30 (WRKY30), Zinc finger of Arabidopsis thaliana 6 (ZAT6) and the ROS-scavenging enzyme Ascorbate peroxidase 2 (APX2). In conclusion, these results indicate that LlHsfA4 plays important roles in heat stress response through regulating the ROS metabolism in lilies.

As worldwide warming intensifies, the average temperature of the earth continues to increase. Temperature is a key factor for the growth and development of all organisms and governs the distribution and seasonal behavior of plants. High temperatures lead to various biochemical, physiological, and morphological changes in plants and threaten plant productivity. As sessile organisms, plants are subjected to various hostile environmental factors and forced to change their cellular state and morphological architecture to successfully deal with the damage they suffer. Therefore, plants have evolved multiple strategies to cope with an abnormal rise in temperature. There are two main mechanisms by which plants respond to elevated environmental temperatures. One is the heat stress response, which is activated under extremely high temperatures; the other is the thermomorphogenesis response, which is activated under moderately elevated temperatures, below the heat-stress range. In this review, we summarize recent progress in the study of these two important heat-responsive molecular regulatory pathways mediated, respectively, by the Heat Shock Transcription Factor (HSF)–Heat Shock Protein (HSP) pathway and PHYTOCHROME INTER-ACTING FACTOR 4 (PIF4) pathways in plants and elucidate the regulatory mechanisms of the genes involved in these pathways to provide comprehensive data for researchers studying the heat response. We also discuss future perspectives in this field.

Intercropping can effectively control some plant soil-borne diseases. However, few studies on intercropping have focused on forage grass as companion plants. In this experiment, Festuca arundinacea (tall fescue) was selected as the intercropping forage to explore whether it could control tomato stem rot. We found that: (1) tomato intercropped with tall fescue had a significantly lower disease incidence and disease index of tomato stem rot than sole tomato; (2) the antifungal activities of the root exudates of tomato and tall fescue in intercropping system were significantly higher than those of sole tomato or tall fescue. Meanwhile, it was inferred that the main allelochemicals might be cyclohexane-1, 2-diol and putrescine based on the GC-MS analysis of root exudates of tall fescue. (3) RNA-seq suggested that intercropping with tall fescue significantly upregulated the expression of genes related to pathogenesis-related proteins and hormone metabolism of tomato compared to those in sole tomato.