Limited nitrogen availability has cultivar-dependent effects on potato tuber yield and tuber quality traits

StCDF1: A 'jack of all trades' clock output with a central role in regulating potato nitrate reduction activity

Transcription factors of the CYCLING DOF FACTOR (CDF) family activate in potato the SP6A FT tuberization signal in leaves. In modern cultivars, truncated StCDF1.2 alleles override strict SD control by stabilizing the StCDF1 protein, which leads to StCOL1 suppression and impaired activation of the antagonic SP5G paralog. By using DAP-seq and RNA-seq studies, we here show that StCDF1 not only acts as an upstream regulator of the day length pathway but also directly regulates several N assimilation and transport genes. StCDF1 directly represses expression of NITRATE REDUCTASE (NR/NIA), which catalyses the first reduction step in nitrate assimilation, and is encoded by a single potato locus. StCDF1 knock-down lines performed better in N-limiting conditions, and this phenotype correlated with derepressed StNR expression. Also, deletion of the StNR DAP-seq region abolished repression by StCDF1, while it did not affect NLP7-dependent activation of the StNR promoter. We identified multiple nucleotide polymorphisms in the DAP-seq region in potato cultivars with early StCDF1 alleles, suggesting that this genetic variation was selected as compensatory mechanism to the negative impact of StCDF1 stabilization. Thereby, directed modification of the StCDF1-recognition elements emerges as a promising strategy to enhance limiting StNR activity in potato.

Potato growth, nitrogen balance, quality, and productivity response to water-nitrogen regulation in a cold and arid environment

Background

The pervasively imprudent practices of irrigation and nitrogen (N) application within Oasis Cool Irrigation zones have led to significant soil nitrogen loss and a marked decrease in water and nitrogen use efficiency.

Methods

To address this concern, a comprehensive field experiment was conducted from April to September in 2023 to investigate the impact of varying degrees of water and fertilization regulation strategies on pivotal parameters including potato yield, quality, nitrogen balance, and water-nitrogen use efficiency. The experimental design incorporated two water deficit degrees at potato seedling (W1, 55%-65% of Field Capacity (FC); W2, 45%-55% of FC), and four distinct nitrogen application gradients (N0, 0 kg ha-1 of N; N1, 130 kg ha-1 of N; N2, 185 kg ha-1 of N; N3, 240 kg ha-1 of N). A control was also included, comprising N0 nitrogen application and full irrigation (W0, 65%-75% of FC), totally eight treatments and one check.

Results

The results indicated that the tuber yield, plant dry matter accumulation, plant height, plant stem, and leaf area index increased with higher nitrogen fertilizer application and irrigation volume. However, tuber starch content, vitamin C, and protein content initially increased and then decreased, while reducing sugar content consistently decreased. Except for W1N2 treatment, the irrigation water use efficiency increased as the N application rate rose, while the nitrogen partial factor productivity, crop nitrogen use efficiency and soil nitrogen use efficiency decreased with an increase in N fertilizer application. The W1N2 treatment resulted in a higher yield (43.16 t ha-1), highest crop nitrogen use efficiency (0.95) and systematic nitrogen use efficiency (0.72),while maintaining moderate levels of soil nitrate and ammonium nitrogen.

Conclusion

Therefore, through the construction of an integrated evaluation index (IEI), the W1N2 treatment of mild water deficit (55%-65% of FC) at potato seedling combined with the medium nitrogen application (185 kg ha-1 of N) has the highest IEI (0.978), it was recommended as the optimal water-nitrogen regulation and management strategies to facilitate high-yield, high-efficiency, and environmentally sustainable potato production in the cold and arid oasis areas of northwest China.

Yield reduction caused by elevated temperatures and high nitrogen fertilization is mitigated by SP6A overexpression in potato (Solanum tuberosum L.)

Potatoes (Solanum tuberosum L.) are a fundamental staple for millions of people worldwide. They provide essential amino acids, vitamins, and starch - a vital component of the human diet, providing energy and serving as a source of fiber. Unfortunately, global warming is posing a severe threat to this crop, leading to significant yield losses, and thereby endangering global food security. Industrial agriculture traditionally relies on excessive nitrogen (N) fertilization to boost yields. However, it remains uncertain whether this is effective in combating heat-related yield losses of potato. Therefore, our study aimed to investigate the combinatory effects of heat stress and N fertilization on potato tuber formation. We demonstrate that N levels and heat significantly impact tuber development. The combination of high N and heat delays tuberization, while N deficiency initiates early tuberization, likely through starvation-induced signals, independent of SELF-PRUNING 6A (SP6A), a critical regulator of tuberization. We also found that high N levels in combination with heat reduce tuber yield rather than improve it. However, our study revealed that SP6A overexpression can promote tuberization under these inhibiting conditions. By utilizing the excess of N for accumulating tuber biomass, SP6A overexpressing plants exhibit a shift in biomass distribution towards the tubers. This results in an increased yield compared to wild-type plants. Our results highlight the role of SP6A overexpression as a viable strategy for ensuring stable potato yields in the face of global warming. As such, our findings provide insights into the complex factors impacting potato crop productivity.

Four New Species of Small-Spored Alternaria Isolated from Solanum tuberosum and S. lycopersicum in China

Small-spored Alternaria species have been frequently isolated from diseased leaves of Solanum plants. To clarify the diversity of small-spored Alternaria species, a total of 118 strains were obtained from leaf samples of S. tuberosum and S. lycopersicum in six provinces of China during 2022-2023. Based on morphological characterization and multi-locus phylogenetic analysis of the internal transcribed spacer of the rDNA region (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), translation elongation factor 1 alpha (TEF1), RNA polymerase second largest subunit (RPB2), Alternaria major allergen gene (Alt a 1), endopolygalacturonase gene (EndoPG) and an anonymous gene region (OPA10-2), seven species were determined, including four novel species and three known species (A. alternata, A. gossypina and A. arborescens). The novel species were described and illustrated as A. longxiensis sp. nov., A. lijiangensis sp. nov., A. lycopersici sp. nov. and A. solanicola sp. nov.. In addition, the pathogenicity of the seven species was evaluated on potato leaves. The species exhibited various aggressiveness, which could help in disease management.

Transcriptome analysis and phenotyping of walnut seedling roots under nitrogen stresses

Nitrogen is an essential core element in walnut seedling growth and development. However, nitrogen starvation and excessive nitrogen stress can cause stunted growth and development of walnut seedlings, and environmental pollution is also of concern. Therefore, it is necessary to study the mechanism of walnut seedling resistance to nitrogen stress. In this study, morphological and physiological observations and transcriptome sequencing of walnut seedlings under nitrogen starvation and excess nitrogen stress were performed. The results showed that walnut seedlings under nitrogen starvation and excess stress could adapt to the changes in the nitrogen environment by changing the coordination of their root morphology and physiological indexes. Based on an analysis of transcriptome data, 4911 differential genes (DEGs) were obtained (2180 were upregulated and 2731 were downregulated) in a comparison of nitrogen starvation and control groups. A total of 9497 DEGs (5091 upregulated and 4406 downregulated) were obtained in the comparison between the nitrogen overdose and control groups. When these DEGs were analysed, the differential genes in both groups were found to be significantly enriched in the plant’s circadian pathway. Therefore, we selected the circadian rhythm as the focus for further analysis. We made some discoveries by analysing the gene co-expression network of nitrogen metabolism, circadian rhythm, and hormone signal transduction. (a) Nitrite nitrogen (NO₂⁻) or Glu may act as a nitrogen signal to the circadian clock. (b) Nitrogen signalling may be input into the circadian clock by regulating changes in the abundance of the CRY1 gene. (c) After the nitrogen signal enters the circadian clock, the expression of the LHY gene is upregulated, which causes a phase shift in the circadian clock. (d) The RVE protein may send information about the circadian clock’s response to nitrogen stress back to the nitrogen metabolic pathway via the hormone transduction pathway. In conclusion, various metabolic pathways in the roots of walnut seedlings coordinated with one another to resist the ill effects of nitrogen stress on the root cells, and these coordination relationships were regulated by the circadian clock. This study is expected to provide valuable information on the circadian clock regulation of plant resistance to nitrogen stress.

Rhizosphere Microbiomes of Potato Cultivated under Bacillus subtilis Treatment Influence the Quality of Potato Tubers

Plants serve as a niche for the growth and proliferation of a diversity of microorganisms. Soil microorganisms, which closely interact with plants, are increasingly being recognized as factors important to plant health. In this study, we explored the use of high-throughput DNA sequencing of the fungal ITS and bacterial 16S for characterization of the fungal and bacterial microbiomes following biocontrol treatment (DT) with Bacillus subtilis strain Bv17 relative to treatments without biocontrol (DC) during the potato growth cycle at three time points. A total of 5631 operational taxonomic units (OTUs) were identified from the 16S data, and 2236 OTUs were identified from the ITS data. The number of bacterial and fungal OTU in DT was higher than in DC and gradually increased during potato growth. In addition, indices such as Ace, Chao, Shannon, and Simpson were higher in DT than in DC, indicating greater richness and community diversity in soil following the biocontrol treatment. Additionally, the potato tuber yields improved without a measurable change in the bacterial communities following the B. subtilis strain Bv17 treatment. These results suggest that soil microbial communities in the rhizosphere are differentially affected by the biocontrol treatment while improving potato yield, providing a strong basis for biocontrol utilization in crop production.

Maize Straw Return and Nitrogen Rate Effects on Potato (Solanum tuberosum L.) Performance and Soil Physicochemical Characteristics in Northwest China

The average yield of fresh potato tubers per hectare is relatively low in China, partly due to poor nutrient management. Chronic inorganic N enrichment leads to soil acidification, which deteriorates soil fertility. Straw residues are removed from the field or burnt during land preparation, resulting in nutrient depletion and air pollution. However, these residues can be returned to the soil to improve its fertility. Therefore, a two–year experiment was conducted in an existing field with five years of different inorganic nitrogen (N) rate to determine the effects of straw return and N rate on potato growth, tuber yield, and quality, profit margin, and soil physicochemical properties. The experiment consisted of four N rates: 0 (control, CK), 75 (low N rate, LN), 150 (medium N rate, MN), and 300 (high N rate, HN) kg N ha−1 with and without straw (9 t ha−1) return. The results showed that straw with N enrichment improved soil fertility, which increased tuber yield and quality. Compared to the control, MN + straw treatment stimulated economic tuber yield (34.73% and 38.34%), profit margin (55.51% and 63.03%), and protein content (20.04% and 25.46%) in 2018 and 2019, respectively. Nitrogen enrichment after straw return is a sustainable practice for stimulating potato tuber yield, profit margin, and improving soil fertility to promote sustainable agriculture development.

Developmental stage-specific metabolite signatures in Arabidopsis thaliana under optimal and mild nitrogen limitation

Metabolites influence flowering time, and thus are among the major determinants of yield. Despite the reported role of trehalose 6-phosphate and nitrate signaling on the transition from the vegetative to the reproductive phase, little is known about other metabolites contributing and responding to developmental phase changes. To increase our understanding which metabolic traits change throughout development in Arabidopsis thaliana and to identify metabolic markers for the vegetative and reproductive phases, especially among individual amino acids (AA), we profiled metabolites of plants grown in optimal (ON) and limited nitrogen (N) (LN) conditions, the latter providing a mild but consistent limitation of N. We found that although LN plants adapt their growth to a decreased level of N, their metabolite profiles are strongly distinct from ON plant profiles, with N as the driving factor for the observed differences. We demonstrate that the vegetative and the reproductive phase are not only marked by growth parameters such as biomass and rosette area, but also by specific metabolite signatures including specific single AA. In summary, we identified N-dependent and -independent indicators manifesting developmental stages, indicating that the plant's metabolic status also reports on the developmental phases.

Synchronization of developmental, molecular and metabolic aspects of source-sink interactions

Plants have evolved a multitude of strategies to adjust their growth according to external and internal signals. Interconnected metabolic and phytohormonal signalling networks allow adaption to changing environmental and developmental conditions and ensure the survival of species in fluctuating environments. In agricultural ecosystems, many of these adaptive responses are not required or may even limit crop yield, as they prevent plants from realizing their fullest potential. By lifting source and sink activities to their maximum, massive yield increases can be foreseen, potentially closing the future yield gap resulting from an increasing world population and the transition to a carbon-neutral economy. To do so, a better understanding of the interplay between metabolic and developmental processes is required. In the past, these processes have been tackled independently from each other, but coordinated efforts are required to understand the fine mechanics of source-sink relations and thus optimize crop yield. Here, we describe approaches to design high-yielding crop plants utilizing strategies derived from current metabolic concepts and our understanding of the molecular processes determining sink development.

Flowering time and the identification of floral marker genes in Solanum tuberosum ssp. andigena

Solanaceae is a family of flowering plants that includes agricultural species such as tomato (Solanum lycopersicum), eggplant (S. melongena), pepper (Capsicum annuum), and potato (S. tuberosum). The transition from the vegetative to reproductive stage has been extensively investigated in tomato as it affects fruit yield. While potato has mainly been studied with regards to the formation of storage organs, control of flowering time is a subject of increasing interest as development of true seeds is becoming more important for future breeding strategies. Here, we describe a robust growth regime for synchronized development of S. tuberosum ssp. andigena. Using SEM to analyse the developmental stages of the shoot apical meristem (SAM) throughout the floral transition, we show that andigena is a facultative long-day plant with respect to flowering. In addition, we identify the flower meristem identity gene MACROCALYX (StMC) as a marker to distinguish between the vegetative and reproductive stages. We show that the expression of WUSCHEL HOMEOBOX 9 (StWOX9) and ANANTHA (StAN) are specific to the inflorescence meristem and flower meristems in the cyme, respectively. The expression patterns of homologs of Arabidopsis flowering-time regulators were studied, and indicated that SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (StSOC1) and StFD might regulate flowering similar to other plant species.