Optimum root zone temperature of photosynthesis and plant growth depends on air temperature in lettuce plants.

KEY MESSAGE: The present study clearly showed that the optimum root zone temperature of photosynthesis and plant growth was affected by air temperature, and that optimization of root zone temperature depending on an air growth temperature by cooling systems could lead to improvement of plant production. Temperature is one of the critical factors affecting plant growth and yield production. Both air and root zone temperatures can strongly affect growth and development of plants. However, studies on the effects of root zone temperature on plant growth parameters along with air temperature are still limited. In the present study, the effects of air and root zone temperature on plant growth, physiological parameters and photosynthetic characteristics of lettuce plants were investigated to optimize the air and root zone temperature to achieve the best growth conditions for lettuce plants. Two air temperature treatments (30/25 and 25/20 °C at day/night temperature) and five root zone temperature treatments (15, 20, 25, 30 and 35 °C) were applied in this study. The present study showed that the maximum plant growth of lettuce plants was higher in air temperatures at 30/25 °C than in 25/20 °C. When the plants were grown at an air temperature of 30/25 °C, the optimum root zone temperature appeared to be 30 °C. However, when the plants were grown at an air temperature of 25/20 °C, the optimum root temperature decreased and appeared to be 25 °C. Furthermore, plants grown under air temperature of 30/25 °C showed greater CO2 assimilation rate, stomatal conductance, electron transport rate (ETR) at high light, and lower non-photochemical quenching (NPQ) at high light than those of 25/20 °C. These results suggest that it is necessary to control and adjust the root zone temperature based on the air temperature.

Genome-wide transcriptional analysis of submerged lotus reveals cooperative regulation and gene responses.

Flooding severely limits plant growth even for some aquatic plants. Although much work has been done on submergence response of some important crop plants, little is known about the response mechanism of aquatic plants, i.e. lotus (Nelumbo nucifera). In this study, we investigated the genome-wide regulation lotus genes in response to submergence stress by high-throughput mRNA sequencing. A total of 4002 differentially expressed genes (DEGs) in lotus upon submergence stress. Among them, 1976 genes were up-regulated and 2026 down-regulated. Functional annotation of these genes by Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis revealed that they were mainly involved in processes of oxidation-reduction, abiotic stimuli, cellular metabolism and small molecule metabolism. Based on these data, previous work and quantitative RT-PCR (RT-qPCR) validation, we constructed a cooperative regulation network involved in several important DEGs in regards to the antioxidant system, disease resistance, hypoxia resistance and morphological adaptation. Further work confirmed that several innate immunity genes were induced during submergence and might confer higher resistance to lotus rot disease. In conclusion, these results provide useful information on molecular mechanisms underlying lotus responses to submergence stress.

Dissecting Tissue-Specific Transcriptomic Responses from Leaf and Roots under Salt Stress in Petunia hybrida Mitchell.

One of the primary objectives of plant biotechnology is to increase resistance to abiotic stresses, such as salinity. Salinity is a major abiotic stress and increasing crop resistant to salt continues to the present day as a major challenge. Salt stress disturbs cellular environment leading to protein misfolding, affecting normal plant growth and causing agricultural losses worldwide. The advent of state-of-the-art technologies such as high throughput mRNA sequencing (RNA-seq) has revolutionized whole-transcriptome analysis by allowing, with high precision, to measure changes in gene expression. In this work, we used tissue-specific RNA-seq to gain insight into the Petunia hybrida transcriptional responses under NaCl stress using a controlled hydroponic system. Roots and leaves samples were taken from a continuum of 48 h of acute 150 mM NaCl. This analysis revealed a set of tissue and time point specific differentially expressed genes, such as genes related to transport, signal transduction, ion homeostasis as well as novel and undescribed genes, such as Peaxi162Scf00003g04130 and Peaxi162Scf00589g00323 expressed only in roots under salt stress. In this work, we identified early and late expressed genes in response to salt stress while providing a core of differentially express genes across all time points and tissues, including the trehalose-6-phosphate synthase 1 (TPS1), a glycosyltransferase reported in salt tolerance in other species. To test the function of the novel petunia TPS1 allele, we cloned and showed that TPS1 is a functional plant gene capable of complementing the trehalose biosynthesis pathway in a yeast tps1 mutant. The list of candidate genes to enhance salt tolerance provided in this work constitutes a major effort to better understand the detrimental effects of salinity in petunia with direct implications for other economically important Solanaceous species.

Insight into the evolution of the Solanaceae from the parental genomes of Petunia hybrida.

Petunia hybrida is a popular bedding plant that has a long history as a genetic model system. We report the whole-genome sequencing and assembly of inbred derivatives of its two wild parents, P. axillaris N and P. inflata S6. The assemblies include 91.3% and 90.2% coverage of their diploid genomes (1.4 Gb; 2n = 14) containing 32,928 and 36,697 protein-coding genes, respectively. The genomes reveal that the Petunia lineage has experienced at least two rounds of hexaploidization: the older gamma event, which is shared with most Eudicots, and a more recent Solanaceae event that is shared with tomato and other solanaceous species. Transcription factors involved in the shift from bee to moth pollination reside in particularly dynamic regions of the genome, which may have been key to the remarkable diversity of floral colour patterns and pollination systems. The high-quality genome sequences will enhance the value of Petunia as a model system for research on unique biological phenomena such as small RNAs, symbiosis, self-incompatibility and circadian rhythms.

Transcriptomic analysis of Petunia hybrida in response to salt stress using high throughput RNA sequencing.

Salinity and drought stress are the primary cause of crop losses worldwide. In sodic saline soils sodium chloride (NaCl) disrupts normal plant growth and development. The complex interactions of plant systems with abiotic stress have made RNA sequencing a more holistic and appealing approach to study transcriptome level responses in a single cell and/or tissue. In this work, we determined the Petunia transcriptome response to NaCl stress by sequencing leaf samples and assembling 196 million Illumina reads with Trinity software. Using our reference transcriptome we identified more than 7,000 genes that were differentially expressed within 24 h of acute NaCl stress. The proposed transcriptome can also be used as an excellent tool for biological and bioinformatics in the absence of an available Petunia genome and it is available at the SOL Genomics Network (SGN) http://solgenomics.net. Genes related to regulation of reactive oxygen species, transport, and signal transductions as well as novel and undescribed transcripts were among those differentially expressed in response to salt stress. The candidate genes identified in this study can be applied as markers for breeding or to genetically engineer plants to enhance salt tolerance. Gene Ontology analyses indicated that most of the NaCl damage happened at 24 h inducing genotoxicity, affecting transport and organelles due to the high concentration of Na+ ions. Finally, we report a modification to the library preparation protocol whereby cDNA samples were bar-coded with non-HPLC purified primers, without affecting the quality and quantity of the RNA-seq data. The methodological improvement presented here could substantially reduce the cost of sample preparation for future high-throughput RNA sequencing experiments.