Altered Expression of OsNLA1 Modulates Pi Accumulation in Rice (Oryza sativa L.) Plants

Dehydration-Responsive Element Binding Protein 1C, 1E, and 1G Promote Stress Tolerance to Chilling, Heat, Drought, and Salt in Rice

The dehydration-responsive element binding protein 1 (DREB1)/C-repeat-binding factor (CBF) genes are key regulators of cold acclimation and freezing tolerance in the chilling tolerant Arabidopsis thaliana. Here, we investigated the function of three members of the 10 rice DREB1 genes, OsDREB1C, E, and G, in the chilling sensitive rice plants. Their loss of function (LOF) mutants were each more chilling susceptible compared to the wild type, and the LOF mutants of all three genes, dreb1ceg, were more chilling susceptible than any of the single mutants. Strikingly, these mutants were capable of cold acclimation, indicating that these rice DREB1 genes are important for basal chilling tolerance but not cold acclimation. Transcriptome and physiology analyses suggest that the OsDREB1C/E/G genes are involved in reactive oxygen species (ROS) scavenging and cell death regulation under chilling. Furthermore, these three rice DREB1 genes are found to promote tolerance to other abiotic stresses: the OsDREB1C/E/G genes are positive regulators of heat tolerance, OsDREB1C and OsDREB1G are positive regulators of salt tolerance, and OsDREB1G is a positive regulator of drought tolerance. These findings expand our knowledge of the roles of DREB1 proteins in plants, enhance our mechanistic understanding of abiotic stress tolerance and will facilitate the generation of stress-tolerant crop plants.

Genome-wide identification and characterization of SPX-domain-containing protein gene family in Solanum lycopersicum

The SYG1, PHO81, and XPR1 (SPX) domain is named after the suppressor of yeast gpa1 (Syg1), yeast phosphatase (Pho81) and the human Xenotropic and Polytrophic Retrovirus receptor1 (XPR1). SPX-domain-containing proteins play pivotal roles in maintaining phosphate ions (Pi) homeostasis in plant. This study was to genome-wide identification and analysis of Solanum lycopersicum SPX-domain-containing protein gene family. The Solanum lycopersicum genome contains 19 SPX-domain-containing protein genes. These SPX-domain-containing protein genes were located in seven of the 12 chromosomes. According to the different conserved domains, the proteins encoded by those genes could be divided into four SPX-domain-containing protein families, which included SPX Family, SPX-ERD1/XPR1/SYG1(SPX-EXS) Family, SPX-Major Facilitator Superfamily (SPX-MFS) Family and SPX-Really Interesting New Gene (SPX-RING) Family. Phylogenetic analysis of SPX-domain-containing protein genes in Arabidopsis thaliana, Solanum tuberosum, Capsicum annuum and Solanum lycopersicum classified these genes into eight clades. Expression profiles derived from transcriptome (RNA-seq) data analysis showed 19 SPX-domain-containing protein genes displayed various expression patterns. SPX-domain-containing protein may play different roles in phosphate nutrition of Solanum lycopersicum different tissues and development stages. And, this study can provide the selection of candidate genes for functional research and genome editing in Solanum lycopersicum phosphate ions (Pi) nutrition.

Low nitrogen availability inhibits the phosphorus starvation response in maize (Zea mays ssp. mays L.)

BACKGROUND

Nitrogen (N) and phosphorus (P) are macronutrients essential for crop growth and productivity. In cultivated fields, N and P levels are rarely sufficient, contributing to the gap between realized and potential production. Fertilizer application increases nutrient availability, but is not available to all farmers, nor are current rates of application sustainable or environmentally desirable. Transcriptomic studies of cereal crops have revealed dramatic responses to either low N or low P single stress treatments. In the field, however, levels of both N and P may be suboptimal. The interaction between N and P starvation responses remains to be fully characterized.

RESULTS

We characterized growth and root and leaf transcriptomes of young maize plants under nutrient replete, low N, low P or combined low NP conditions. We identified 1555 genes to respond to our nutrient treatments, in one or both tissues. A large group of genes, including many classical P starvation response genes, were regulated antagonistically between low N and P conditions. An additional experiment over a range of N availability indicated that a mild reduction in N levels was sufficient to repress the low P induction of P starvation genes. Although expression of P transporter genes was repressed under low N or low NP, we confirmed earlier reports of P hyper accumulation under N limitation.

CONCLUSIONS

Transcriptional responses to low N or P were distinct, with few genes responding in a similar way to the two single stress treatments. In combined NP stress, the low N response dominated, and the P starvation response was largely suppressed. A mild reduction in N availability was sufficient to repress the induction of P starvation associated genes. We conclude that activation of the transcriptional response to P starvation in maize is contingent on N availability.

Upstream Open Reading Frame and Phosphate-Regulated Expression of Rice OsNLA1 Controls Phosphate Transport and Reproduction

Rice (Oryza sativa) OsNLA1 has been proposed to play a crucial role in regulating phosphate (Pi) acquisition in roots, similar to that of Arabidopsis (Arabidopsis thaliana) AtNLA. However, unlike AtNLA, OsNLA1 is not a target of miR827, a Pi starvation-induced microRNA. It is, therefore, of interest to know whether the expression of OsNLA1 depends on Pi supply and how it is regulated. In this study, we provide evidence that OsNLA1 controls Pi acquisition by directing the degradation of several OsPHT1 Pi transporters (i.e. OsPT1/2/4/7/8/12). We further show that OsNLA1 has an additional function in reproduction and uncover the mechanism of its expression regulation. Analysis of mRNA levels, promoter-GUS activity, and protoplast transient expression showed that the expression of OsNLA1.1, the most abundant transcript variant, is up-regulated in response to increasing Pi supply. The OsNLA1 promoter region was found to contain an upstream open reading frame that is required for Pi-responsive expression regulation. OsNLA1 promoter activity was observed in roots, ligules, leaves, sheaths, pollen grains, and surrounding the vascular tissues of anthers, suggesting that OsNLA1 is important throughout the development of rice. Disruption of OsNLA1 resulted in increased Pi uptake from roots as well as impaired pollen development and reduced grain production. In summary, our study reveals that Pi-induced OsNLA1 expression regulated by a unique mechanism functions in Pi acquisition, Pi translocation, and reproductive success.

The role of OsNLA1 in regulating arsenate uptake and tolerance in rice

Arsenic (As) contamination in agricultural soil can cause phytotoxicity and lead to As accumulation in crops. Rice (Oryza sativa) feeds half of the world's population, but the molecular mechanism of As detoxification is not well understood in rice. In this study, the role of OsNLA1 in arsenate uptake and tolerance in rice was analyzed. OsNLA1 expression was induced in response to As(V) stress. The osnla1 mutant was more sensitive to As(V) stress than those of the wild type (WT). When exposed to As(V), mutation of OsNLA1 resulted in 30% greater As accumulation in roots and shoots of the WT. Although OsPT8 expression was induced after As(V) exposure, the amount of its protein was reduced. Unexpectedly, the osnla1 mutant showed a significant increase in punctate structures of OsPT8-GFP in response to As(V) stress, while the amount of the OsPT8-GFP protein in the osnla1 mutant was greater than in the WT. Combining OsNLA1 mutation with OsPT8 overexpression resulted in As(V) hypersensitivity, As hyperaccumulation, and higher shoot to root ratio of As in rice. These results indicated that OsNLA1 plays an important role in arsenate uptake and tolerance, mainly via regulating the amount of Pi transporters.

Characterization of the rice NLA family reveals a key role for OsNLA1 in phosphate homeostasis

BACKGROUND

Phosphate (Pi), an essential mineral nutrient for plant development and reproduction, is one of the main components of fertilizers in modern agriculture. Previous research demonstrated that AtNLA1 mediates ubiquitination of Pi transporters in the plasma membrane and triggers their endocytosis and degradation in Arabidopsis. In this study, we researched the function of NLA homologous proteins in Pi homeostasis in rice.

FINDINGS

Two OsNLA homologs from rice (Oryza sativa L.) were identified by bioinformatics and phylogenetic analysis and designated OsNLA1 and OsNLA2. The OsNLA1 clustered with Arabidopsis AtNLA1, was expressed higher than OsNLA2 and was transcriptionally repressed under Pi-deficient condition. Loss-of-function of OsNLA1 caused P overaccumulation and growth inhibitions in both root and shoot under Pi-sufficient condition. Furthermore, mutation of OsNLA1 affected expression of Pi tranporters and root hair development under Pi-sufficient and/or Pi-deficient conditions.

CONCLUSIONS

OsNLA1 plays a key role in maintaining phosphate homeostasis in rice.