Overexpression of OsPHR3 improves growth traits and facilitates nitrogen use efficiency under low phosphate condition

OsbZIP1 regulates phosphorus uptake and nitrogen utilization, contributing to improved yield

Increasing nutrient uptake and use efficiency in plants can contribute to improved crop yields and reduce the demand for fertilizers in crop production. In this study, we characterized a rice mutant, 88n which showed long roots under low nitrogen (N) or phosphorus (P) conditions. Low expression levels of N transporter genes were observed in 88n root, and total N concentration in 88n shoots were decreased, however, C concentrations and shoot dry weight in 88n were comparable to that in WT. Therefore, 88n showed high nitrogen utilization efficiency (NUtE). mRNA accumulation of Pi transporter genes was higher in 88n roots, and Pi concentration and uptake activity were higher in 88n than in WT. Therefore, 88n also showed high phosphorus uptake efficiency (PUpE). Molecular genetic analysis revealed that the causal gene of 88n phenotypes was OsbZIP1, a monocot-specific ortholog of the A. thaliana bZIP transcription factor HY5. Similar to the hy5 mutant, chlorophyll content in roots was decreased and root angle was shallower in 88n than in WT. Finally, we tested the yield of 88n in paddy fields over 3 years because 88n mutant plants showed higher PUpE and NUtE activity and different root architecture at the seedling stage. 88n showed large panicles and increased panicle weight/plant. Taken together, a mutation in OsbZIP1 could contribute to improved crop yields.

The MYB-CC Transcription Factor PHOSPHATE STARVATION RESPONSE-LIKE 7 (PHL7) Functions in Phosphate Homeostasis and Affects Salt Stress Tolerance in Rice

Inorganic phosphate (Pi) homeostasis plays an important role in plant growth and abiotic stress tolerance. Several MYB-CC transcription factors involved in Pi homeostasis have been identified in rice (Oryza sativa). PHOSPHATE STARVATION RESPONSE-LIKE 7 (PHL7) is a class II MYC-CC protein, in which the MYC-CC domain is located at the N terminus. In this study, we established that OsPHL7 is localized to the nucleus and that the encoding gene is induced by Pi deficiency. The Pi-responsive genes and Pi transporter genes are positively regulated by OsPHL7. The overexpression of OsPHL7 enhanced the tolerance of rice plants to Pi starvation, whereas the RNA interference-based knockdown of this gene resulted in increased sensitivity to Pi deficiency. Transgenic rice plants overexpressing OsPHL7 produced more roots than wild-type plants under both Pi-sufficient and Pi-deficient conditions and accumulated more Pi in the shoots and roots. In addition, the overexpression of OsPHL7 enhanced rice tolerance to salt stress. Together, these results demonstrate that OsPHL7 is involved in the maintenance of Pi homeostasis and enhances tolerance to Pi deficiency and salt stress in rice.

Molecular mechanisms and genetic improvement of low-phosphorus tolerance in rice

Phosphorus (P) is a macronutrient required for plant growth and reproduction. Orthophosphate (Pi), the preferred P form for plant uptake, is easily fixed in the soil, making it unavailable to plants. Limited phosphate rock resources, low phosphate fertilizer use efficiency and high demands for green agriculture production make it important to clarify the molecular mechanisms underlying plant responses to P deficiency and to improve plant phosphate efficiency in crops. Over the past 20 years, tremendous progress has been made in understanding the regulatory mechanisms of the plant P starvation response. Here, we systematically review current research on the mechanisms of Pi acquisition, transport and distribution from the rhizosphere to the shoot; Pi redistribution and reuse during reproductive growth; and the molecular mechanisms of arbuscular mycorrhizal symbiosis in rice (Oryza sativa L.) under Pi deficiency. Furthermore, we discuss several strategies for boosting P utilization efficiency and yield in rice.

Plant adaptation to low phosphorus availability: Core signaling, crosstalks, and applied implications

Phosphorus (P) is an essential nutrient for plant growth and reproduction. Plants preferentially absorb P as orthophosphate (Pi), an ion that displays low solubility and that is readily fixed in the soil, making P limitation a condition common to many soils and Pi fertilization an inefficient practice. To cope with Pi limitation, plants have evolved a series of developmental and physiological responses, collectively known as the Pi starvation rescue system (PSR), aimed to improve Pi acquisition and use efficiency (PUE) and protect from Pi-starvation-induced stress. Intensive research has been carried out during the last 20 years to unravel the mechanisms underlying the control of the PSR in plants. Here we review the results of this research effort that have led to the identification and characterization of several core Pi starvation signaling components, including sensors, transcription factors, microRNAs (miRNAs) and miRNA inhibitors, kinases, phosphatases, and components of the proteostasis machinery. We also refer to recent results revealing the existence of intricate signaling interplays between Pi and other nutrients and antagonists, N, Fe, Zn, and As, that have changed the initial single-nutrient-centric view to a more integrated view of nutrient homeostasis. Finally, we discuss advances toward improving PUE and future research priorities.

Meta-QTLs, ortho-MQTLs and candidate genes for nitrogen use efficiency and root system architecture in bread wheat (Triticum aestivum L.)

In wheat, meta-QTLs (MQTLs), ortho-MQTLs, and candidate genes (CGs) were identified for nitrogen use efficiency and root system architecture. For this purpose, 1788 QTLs were available from 24 studies published during 2006-2020. Of these, 1098 QTLs were projected onto the consensus map resulting in 118 MQTLs. The average confidence interval (CI) of MQTLs was reduced up to 8.56 folds in comparison to the average CI of QTLs. Of the 118 MQTLs, 112 were anchored to the physical map of the wheat reference genome. The physical interval of MQTLs ranged from 0.02 to 666.18 Mb with a mean of 94.36 Mb. Eighty-eight of these 112 MQTLs were verified by marker-trait associations (MTAs) identified in published genome-wide association studies (GWAS); the MQTLs that were verified using GWAS also included 9 most robust MQTLs, which are particularly useful for breeders; we call them 'Breeder's QTLs'. Some selected wheat MQTLs were further utilized for the identification of ortho-MQTLs for wheat and maize; 9 such ortho-MQTLs were available. As many as 1991 candidate genes (CGs) were also detected, which included 930 CGs with an expression level of > 2 transcripts per million in relevant organs/tissues. Among the CGs, 97 CGs with functions previously reported as important for the traits under study were selected. Based on homology analysis and expression patterns, 49 orthologues of 35 rice genes were also identified in MQTL regions. The results of the present study may prove useful for the improvement of selection strategy for yield potential, stability, and performance under N-limiting conditions.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01085-0.