Affects Rice Growth Research Articles

Genetic Diversity and Genome-Wide Association Study for Shoot and Root Traits in Rice Grown Under Water Deficit at Early Vegetative Stage

Water deficit affects rice growth, development, and yield. Knowledge of genetic diversity for water deficit tolerance, as well as the genetic architecture that is responsible for this trait, can accelerate rice cultivars’ improvement. In this study, different tools were applied to assess genetic diversity and identify genome regions associated with shoot and root traits in rice germplasm grown under water deficit at an early vegetative stage. A panel of 177 rice genotypes grown under water deficit was evaluated for root length (RL), root dry weight (RDW), shoot length (SL), and shoot dry weight (SDW). Genetic diversity was investigated using means grouping and principal component analysis. For the genome-wide association study, a general linear model was applied, using RL, RDW, SL, and SDW phenotypic data converted into Best Linear Unbiased Prediction (BLUPs); genotypic data (1185 single nucleotide polymorphism—SNPs-loci); and population structure. Overall, little genetic diversity was observed, but genotypes with a higher water deficit tolerance were identified. Several significant SNPs were mapped, 81, 5, 53, and 41 for RL, RDW, SL, and SDW, respectively. Among the identified genes, there are those encoding kinases, proteins involved in phytohormone and cell wall metabolism, and Cytochrome P450. The obtained results provide insight into genetic diversity and the genetic architecture of water deficit tolerance, which will be useful in improving this trait in rice grown in Brazil.

A Leucine-Rich Receptor Like Kinase LRK2 Is Involved in the Regulation of Cold Tolerance and Yield in Rice.

Low temperature affects rice growth and yield. Receptor-like protein kinases play an important role in plant growth and development. In order to reveal the role of a leucine-rich receptor like kinase LRK2 in low temperature stress and growth and development of rice. In this study, we used the obtained LRK2 overexpressing plants for experiments and the results show that the cold tolerance and yield of LRK2 overexpressing plants were higher than that of wild type. LRK2 has high homology with the phytosulfokine receptors (PSKRs) gene of different species, and LRK2 gene is responsive to phytosulfokine (PSK). In addition, we observed that the proline content of LRK2 overexpressing plants was significantly higher than that of the wild-type at low temperature, while the malondialdehyde content was significantly lower than that of the wild-type. Yeast two-hybrid screening and bimolecular fluorescence complementary analysis showed that LRK2 interacts with rice growth hormone response factor 24 (OsARF24) in vitro. These results suggest that LRK2 gene may be involved in the regulation of cold stress response and yield in rice. These findings will help us understand PSKR signaling in other grasses and support improvements in rice genetics.

Hydroponic Culture of Rice Seedlings for Stress Response Assay.

The major environmental factors limiting rice growth and production are osmotic stresses such as drought and high salinity. High osmotic stresses directly disrupt cellular activities, leading to plant growth retardation or death. Plants have various response mechanisms to survive under such stresses. Understanding rice's stress response mechanisms is necessary to enhance the osmotic stress tolerance of rice. However, assessing specific physiological responses to osmotic stresses is difficult because multiple environmental factors affect rice growth. Here, we describe a simple method for analyzing the osmotic stress responses of rice plants using a hydroponic culture system. This method allows comprehensive gene expression and phenotypic analyses under osmotic stress conditions in rice. Various osmotic stress conditions and samples can be tested simultaneously because this method is small-scale. In addition, the procedure is easy, and highly reproductive results can be obtained.

Microbial decomposer for crop residue management in rice-wheat cropping system.

Crop residue management is vital in the rice-wheat cropping system, influencing soil health and crop productivity. This study examined the effects of organic and inorganic fertilizers and microbial decomposers on rice growth and yield. We evaluated seven treatments: 100% recommended dose fertilizer (RDF); 50% residue + 50% RDF; 50% residue + 50% RDF + Pusa decomposer; 50% residue + 50% green manuring (GM)/green leaf manuring (GLM); 50% residue + 50% GM/GLM + Pusa decomposer; residue @ 2.5 tons per acre + Pusa decomposer; residue @ 2.5 tons per acre + no Pusa decomposer; and absolute control. Results indicate that integrating organic and inorganic fertilizers with microbial decomposers positively affects rice growth and yield parameters. While adding microbial decomposer to RDF did not consistently enhance rice yield, it improved soil enzymatic properties. This suggests that the effectiveness of microbial decomposers may vary based on specific soil and crop conditions. Therefore, microbial decomposers present a promising approach to boost soil health and fertility. Further research is needed to optimize conditions for their use and systematically assess their impact on crop yields.

Prevalence and Characterization of Plant-Parasitic Nematodes Existing in RD41 Rice Fields in Pathum Thani Province, Thailand, with Emphasis on Hirschmanniella mucronata and Meloidogyne graminicola

Plant parasitic nematodes (PPNs) are one of the most destructive pests affecting rice growth worldwide. In this study, populations of PPNs associated with RD41 rice fields in Pathum Thani Province, Thailand, were surveyed and the dominant PPNs found in the fields were identified using a combination of morphological and molecular traits. A total of 105 soil or root samples were taken from 21 paddy fields in 7 districts of Pathum Thani, and nematode extraction was processed in a laboratory. In all sampled rice fields, 6 nematode genera, namely Hirschmanniella sp., Meloidogyne sp., Pratylenchus sp., Tylenchorhynchus sp., Helicotylenchus sp., and Tylenchus sp., were extracted. Of these 6 nematode genera, Hirschmanniella sp. was the most prevalent in both soil and root samples (66.7 - 100 % occurrence observed), followed by Meloidogyne sp., which was found in only 4 districts of the province (0.2 to 8.7 % occurrence observed). The species of these predominant PPNs were morphologically and molecularly characterized. The identification results remained consistent across morphological features and molecular techniques, confirming the presence of Hirschmanniella mucronata and Meloidogyne graminicola in the studied rice fields. The results of this study provide useful baseline data of the occurrence of PPNs in Thailand's rice fields. The incidence of some PPNs found in this study is likely to become a significant factor limiting rice production yields if they are not better managed. HIGHLIGHTS Plant-parasitic nematode (PPN) populations in RD41 rice fields located in Pathum Thani province, Thailand were examined Six PPN genera were extracted from soil and root samples The predominant PPNs were characterized using morphological and molecular traits The main PPNs were identified as mucronata and M. graminicola This study provides useful baseline data of PPNs found in Thailand's rice fields GRAPHICAL ABSTRACT

Mutation of a RING E3 ligase, OsDIRH2, enhances drought tolerance in rice with low stomata density.

Drought is a major environmental stress factor that negatively affects rice growth and yield. From a forward genetic perspective, we selected a drought-insensitive TILLING line (ditl4) from a gamma-ray-induced core mutant population (M10). Under drought conditions, ditl4 exhibited greater fresh weight, survival rate, chlorophyll, proline, and soluble sugar contents, and lower H2O2 and MDA levels than wild-type (WT). In addition, the activities of antioxidant enzymes, such as superoxide dismutase, catalase, and peroxidase, were higher in ditl4 than in the WT. In the relative water loss assay, dilt4 showed significantly decreased leaf curling and water loss compared to WT. Also, the ratio of "closed" stomata aperture was increased in ditl4 under drought stress, suggesting reduced transpiration to prevent water loss. The ditl4 mutant showed decreased stomatal conductance, transpiration, and CO2 assimilation and increased water use efficiency due to the low density of stomata. Whole-genome resequencing analysis of dilt4 identified a single nucleotide polymorphism (SNP) in OsDIRH2 (LOC_Os11g39640), annotated as a RING-H2 type E3 ligase, resulting in a premature stop codon. CRISPR/Cas9-mediated knock-out mutants (OsDIRH2a and OsDIRH2b) enhanced drought tolerance by lowering stomatal density compared to empty vector control plants. These findings suggested that ditl4 with low stomatal density would be useful as a genetic resource for a drought-tolerant breeding program to improve water-use efficiency.

The OsSRO1c-OsDREB2B complex undergoes protein phase transition to enhance cold tolerance in rice

Cold stress is one of the major abiotic stress factors affecting rice growth and development, leading to significant yield loss in the context of global climate change. Exploring natural variants that confer cold resistance and the underlying molecular mechanism responsible for this is the major strategy to breed cold-tolerant rice varieties. Here, we show that natural variations of a SIMILAR to RCD ONE (SRO) gene, OsSRO1c, confer cold tolerance in rice at both seedling and booting stages. Our in vivo and in vitro experiments demonstrated that OsSRO1c possesses intrinsic liquid–liquid phase-separation ability and recruits OsDREB2B, an AP2/ERF transcription factor that functions as a positive regulator of cold stress, into its biomolecular condensates in the nucleus, resulting in elevated transcriptional activity of OsDREB2B. We found that the OsSRO1c-OsDREB2B complex directly responds to low temperature through dynamic phase transitions and regulates key cold-response genes, including COLD1. Furthermore, we showed that introgression of an elite haplotype of OsSRO1c into a cold-susceptible indica rice could significantly increase its cold resistance. Collectively, our work reveals a novel cold-tolerance regulatory module in rice and provides promising genetic targets for molecular breeding of cold-tolerant rice varieties.

Knockout of the Chlorophyll a Oxygenase Gene OsCAO1 Reduces Chilling Tolerance in Rice Seedlings.

Chilling stress is one of the main abiotic factors affecting rice growth and yield. In rice, chlorophyllide a oxygenase encoded by OsCAO1 is responsible for converting chlorophyllide a to chlorophyllide b, playing a crucial role in photosynthesis and thus rice growth. However, little is known about the function of OsCAO1 in chilling stress responses. The presence of the cis-acting element involved in low-temperature responsiveness (LTR) in the OsCAO1 promoter implied that OsCAO1 probably is a cold-responsive gene. The gene expression level of OsCAO1 was usually inhibited by low temperatures during the day and promoted by low temperatures at night. The OsCAO1 knockout mutants generated by the CRISPR-Cas9 technology in rice (Oryza sativa L.) exhibited significantly weakened chilling tolerance at the seedling stage. OsCAO1 dysfunction led to the accumulation of reactive oxygen species and malondialdehyde, an increase in relative electrolyte leakage, and a reduction in antioxidant gene expression under chilling stress. In addition, the functional deficiency of OsCAO1 resulted in more severe damage to chloroplast morphology, such as abnormal grana thylakoid stacking, caused by low temperatures. Moreover, the rice yield was reduced in OsCAO1 knockout mutants. Therefore, the elevated expression of OsCAO1 probably has the potential to increase both rice yield and chilling tolerance simultaneously, providing a strategy to cultivate chilling-tolerant rice varieties with high yields.

Characterization of SIPs-type aquaporins and their roles in response to environmental cues in rice (Oryza sativa L.)

BackgroundAquaporins (AQPs) facilitate water diffusion across biological membranes and are involved in all phases of growth and development. Small and basic intrinsic proteins (SIPs) belong to the fourth subfamily of the plant AQPs. Although SIPs are widely present in higher plants, reports on SIPs are limited. Rice is one of the major food crops in the world, and water use is an important factor affecting rice growth and development; therefore, this study aimed to provide information relevant to the function and environmental response of the rice SIP gene family.ResultsThe rice (Oryza sativa L. japonica) genome encodes two SIP-like genes, OsSIP1 and OsSIP2, whose products are predominantly located in the endoplasmic reticulum (ER) membrane but transient localization to the plasma membrane is not excluded. Heterologous expression in a yeast aquaglyceroporin-mutant fps1Δ showed that both OsSIP1 and OsSIP2 made the cell more sensitive to KCl, sorbitol and H2O2, indicating facilitated permeation of water and hydrogen peroxide. In addition, the yeast cells expressing OsSIP2 were unable to efflux the toxic methylamine taken up by the endogenous MEP permeases, but OsSIP1 showed subtle permeability to methylamine, suggesting that OsSIP1 may have a wider conducting pore than OsSIP2. Expression profiling in different rice tissues or organs revealed that OsSIP1 was expressed in all tissues tested, whereas OsSIP2 was preferentially expressed in anthers and weakly expressed in other tissues. Consistent with this, histochemical staining of tissues expressing the promoter-β-glucuronidase fusion genes revealed their tissue-specific expression profile. In rice seedlings, both OsSIPs were upregulated to varied levels under different stress conditions, including osmotic shock, high salinity, unfavorable temperature, redox challenge and pathogen attack, as well as by hormonal treatments such as GA, ABA, MeJA, SA. However, a reduced expression of both OsSIPs was observed under dehydration treatment.ConclusionsOur results suggest that SIP-like aquaporins are not restricted to the ER membrane and are likely to be involved in unique membrane functions in substrate transport, growth and development, and environmental response.

A calmodulin-like protein PvCML9 negatively regulates salt tolerance

Calmodulin-like proteins (CMLs) are unique Ca2+ sensors and play crucial roles in response to abiotic stress in plants. A salt-repressed PvCML9 from halophyte seashore paspalum (Paspalum vaginatum O. Swartz) was identified. PvCML9 was localized in the cytoplasm and nucleus and highly expressed in roots and stems. Overexpression of PvCML9 led to reduced salt tolerance in rice and seashore paspalum, whereas downregulating expression of PvCML9 showed increased salt tolerance in seashore paspalum as compared with the wild type (WT), indicating that PvCML9 regulated salt tolerance negatively. Na+ and K+ homeostasis was altered by PvCML9 expression. Lower level of Na+/K+ ratio in roots and shoots was maintained in PvCML9-RNAi lines compared with WT under salt stress, but higher level in overexpression lines. Moreover, higher levels of SOD and CAT activities and proline accumulation were observed in PvCML9-RNAi lines compared with WT under salt stress, but lower levels in overexpression lines, which altered ROS homeostasis. Based on the above data, mutation of its homolog gene OsCML9 in rice by CRISPR/Cas9 was performed. The mutant had enhanced salt tolerance without affecting rice growth and development, suggesting that OsCML9 gene is an ideal target gene to generate salt tolerant cultivars by genome editing in the future.

The Oryza sativa transcriptome responds spatiotemporally to polystyrene nanoplastic stress

Nanoplastic represents an emerging abiotic stress facing modern agriculture, impacting global crop production. However, the molecular response of crop plants to this stress remains poorly understood at a spatiotemporal resolution. We therefore used RNA sequencing to profile the transcriptome expressed in rice (Oryza sativa) root and leaf organs at 1, 2, 4, and 8 d post exposure with nanoplastic. We revealed a striking similarity between the rice biomass dynamics in aboveground parts to that in belowground parts during nanoplastic stress, but transcriptome did not. At the global transcriptomic level, a total of 2332 differentially expressed genes were identified, with the majority being spatiotemporal specific, reflecting that nanoplastics predominantly regulate three processes in rice seedlings: (1) down-regulation of chlorophyll biosynthesis, photosynthesis, and starch, sucrose and nitrogen metabolism, (2) activation of defense responses such as brassinosteroid biosynthesis and phenylpropanoid biosynthesis, and (3) modulation of jasmonic acid and cytokinin signaling pathways by transcription factors. Notably, the genes involved in plant-pathogen interaction were shown to be successively modulated by both root and leaf organs, particularly plant disease defense genes (OsWRKY24, OsWRKY53, Os4CL3, OsPAL4, and MPK5), possibly indicating that nanoplastics affect rice growth indirectly through other biota. Finally, we associated biomass phenotypes with the temporal reprogramming of rice transcriptome by weighted gene co-expression network analysis, noting a significantly correlation with photosynthesis, carbon metabolism, and phenylpropanoid biosynthesis that may reflect the mechanisms of biomass reduction. Functional analysis further identified PsbY, MYB, cytochrome P450, and AP2/ERF as hub genes governing these pathways. Overall, our work provides the understanding of molecular mechanisms of rice in response to nanoplastics, which in turn suggests how rice might behave in a nanoplastic pollution scenario.

Improving the prediction performance of leaf water content by coupling multi-source data with machine learning in rice (Oryza sativa L.)

BackgroundLeaf water content (LWC) significantly affects rice growth and development. Real-time monitoring of rice leaf water status is essential to obtain high yield and water use efficiency of rice plants with precise irrigation regimes in rice fields. Hyperspectral remote sensing technology is widely used in monitoring crop water status because of its rapid, nondestructive, and real-time characteristics. Recently, multi-source data have been attempted to integrate into a monitored model of crop water status based on spectral indices. However, there are fewer studies using spectral index model coupled with multi-source data for monitoring LWC in rice plants. Therefore, 2-year field experiments were conducted with three irrigation regimes using four rice cultivars in this study. The multi-source data, including canopy ecological factors and physiological parameters, were incorporated into the vegetation index to accurately predict LWC in rice plants.ResultsThe results presented that the model accuracy of rice LWC estimation after combining data from multiple sources improved by 6–44% compared to the accuracy of a single spectral index normalized difference index (ND). Additionally, the optimal prediction accuracy of rice LWC was produced using a machine algorithm of gradient boosted decision tree (GBDT) based on the combination of ND(1287,1673) and crop water stress index (CWSI) (R2 = 0.86, RMSE = 0.01).ConclusionsThe machine learning estimation model constructed based on multi-source data fully utilizes the spectral information and considers the environmental changes in the crop canopy after introducing multi-source data parameters, thus improving the performance of spectral technology for monitoring rice LWC. The findings may be helpful to the water status diagnosis and accurate irrigation management of rice plants.

Evaluation of Germplasm for Seedling Stage Salinity Tolerance in Rice (Oryza Sativa L.)

Salinity affects rice growth and development. Mostly all growth stages from germination to maturity are affected by the salinity. Among all the stages, seedling and reproductive stages are the most sensitive stages to salinity, which results in considerable yield losses. Development of salt tolerant varieties is most feasible approach for improving the production of rice in salt affected soils as seedling stage is necessary for better crop improvement. Overall 76 rice germplasm lines were evaluated at RARS, Maruteru, West Godavari, A.P during Kharif 2020 for salinity tolerance at seedling stage. The different parameters like root length, shoot length, shoot Na+ content, shoot K+ content, Na+/K+ content and SIS (salt injury score) at 10th and 16th day were studied under hydroponics subjecting to electrical conductivity of 6 and 12 dSm-1, at a pH of 5.0. Salinity scoring during seedling stage was noted as per the modified standard evaluation score (SES) of IRRI, revealed that four genotypes FL478, MTU1290, MTU1061 and MCM109 as tolerant, 23 genotypes as moderately tolerant, 42 were susceptible and remaining seven genotypes namely BPT2848, BPT3140, Hallabhatta, MTU1271, MTU1121, BPT2846 and Krishnahamsa are highly susceptible. The phenotypic study signified that Na+/K+ ratio is the key note for salinity tolerance.

Identification of rice disease under complex background based on PSOC-DRCNet

Rice is a crucial agricultural crop, yet it frequently suffers from various diseases, leading to decreased yields and, in severe cases, crop failure. Diseases significantly affect rice growth and yield, resulting in economic losses and food security challenges. The role of image recognition in identifying rice diseases is critical in agricultural production. It enables automated and efficient detection of rice diseases, which is essential for effective management, ensuring food security and sustainable agriculture. To address issues like background noise and edge blurring in rice disease image capture, as well as challenges in determining the optimal learning rate during the training of traditional rice disease recognition networks, a novel method based on PSOC-DRCNet is proposed for rice disease recognition.. First, tto solve the problem of background interference, Dual Mode Attention (DMA) is proposed to adaptively capture meaningful regions in rice disease images. Second, the Residual Adaptive Block(RAB) is proposed, which utilizes dimensional changes and channel attention to solve edge blur problems. Then, a Cross entropy and regularized mixed Loss function (CerLoss), is proposed to optimize the learning strategy of the model in the process of processing datasets and enhance the performance and generalization ability of the model to avoid overfitting problems. Ultimately, In response to the cumbersome problem of finding the optimal learning rate, we propose using Particle Swarm Optimization Chameleon (PSOC) to find the optimal learning rate and train the PSOC-DRCNet model on our custom dataset and compare it with other existing methods and the final average classification accuracy of PSOC-DRCNet is 93.88% with an F1 score of 0.940. We compare it with other existing methods. It is proved that the average classification accuracy of our model under hyper-parameter unification is 92.65% F1 score is 0.928. We validated the PSOC-DRCNet by conducting comparative analyses with other models and through generalization experiments and module effectiveness tests. Additionally, the practicality of PSOC-DRCNet was confirmed through its application in real-world scenarios. The methods proposed in this paper successfully enable the identification of various diseases in rice leaves, offering a practical solution for incorporating deep learning into the agricultural production process. Furthermore, these findings serve as a valuable reference for disease identification in other crops.

Rational Utilization of Sediment Resources Improves Rice Yield and Nitrogen Use Efficiency under Salt Stress

Soil salinization negatively affects rice growth and yield; however, how different sludge sources regulate rice growth and yield under salt stress was rarely investigated. This study evaluated the performance of two salt-tolerant rice cultivars, Chaoyou 1000 and Longliangyou 506, grown in two sediment sources, pond sediment (PS) and river sludge (RS), under salt stress (56 ds m−1 brine irrigation) with conventional soil (CS) used as the control. The results showed that the rice yield under the PS and RS treatments was enhanced by 51.0% and 43.6% as compared with CS, respectively, owing to an improvement in spikelet per panicle, 1000-grain weight, dry matter accumulation, and the chlorophyll content in both rice cultivars. Compared with CS, the total nitrogen accumulation, nitrogen grain production efficiency, nitrogen harvest index, and nitrogen partial productivity under the PS and RS treatments were increased by 18.9–28.9%, 17.0–20.6%, 7.2–16.6%, and 43.8–50.9%, respectively. Moreover, rice grown in PS and RS showed higher activities of nitrogen metabolism-related enzymes (nitrate reductase, glutamine synthetase, and glutamate synthetase) at the heading stage and higher K+ and K+/Na+ contents in the leaves. Overall, a balanced utilization of sediment resources (especially pond sediment) can effectively alleviate salt stress and improve the yield and nitrogen use efficiency in rice.

OsBCAT2, a gene responsible for the degradation of branched-chain amino acids, positively regulates salt tolerance by promoting the synthesis of vitamin B5.

Salt stress negatively affects rice growth, development and yield. Metabolic adjustments contribute to the adaptation of rice under salt stress. Branched-chain amino acids (BCAA) are three essential amino acids that cannot be synthesized by humans or animals. However, little is known about the role of BCAA in response to salt stress in plants. Here, we showed that BCAAs may function as scavengers of reactive oxygen species (ROS) to provide protection against damage caused by salinity. We determined that branched-chain aminotransferase 2 (OsBCAT2), a protein responsible for the degradation of BCAA, positively regulates salt tolerance. Salt significantly induces the expression of OsBCAT2 rather than BCAA synthesis genes, which indicated that salt mainly promotes BCAA degradation and not de novo synthesis. Metabolomics analysis revealed that vitamin B5 (VB5) biosynthesis pathway intermediates were higher in the OsBCAT2-overexpressing plants but lower in osbcat2 mutants under salt stress. The salt stress-sensitive phenotypes of the osbcat2 mutants are rescued by exogenous VB5, indicating that OsBCAT2 affects rice salt tolerance by regulating VB5 synthesis. Our work provides new insights into the enzymes involved in BCAAs degradation and VB5 biosynthesis and sheds light on the molecular mechanism of BCAAs in response to salt stress.

Molecular Mechanisms and Regulatory Pathways Underlying Drought Stress Response in Rice.

Rice is a staple food for 350 million people globally. Its yield thus affects global food security. Drought is a serious environmental factor affecting rice growth. Alleviating the inhibition of drought stress is thus an urgent challenge that should be solved to enhance rice growth and yield. This review details the effects of drought on rice morphology, physiology, biochemistry, and the genes associated with drought stress response, their biological functions, and molecular regulatory pathways. The review further highlights the main future research directions to collectively provide theoretical support and reference for improving drought stress adaptation mechanisms and breeding new drought-resistant rice varieties.

NIT24 and NIT29-mediated IAA synthesis of Xanthomonas oryzae pv. oryzicola suppresses immunity and boosts growth in rice.

Auxin plays a pivotal role in the co-evolution of plants and microorganisms. Xanthomonas oryzae pv. oryzicola (Xoc) stands as a significant factor that affects rice yield and quality. However, the current understanding of Xoc's capability for indole 3-acetic acid (IAA) synthesis and its mechanistic implications remains elusive. In this study, we performed a comprehensive genomic analysis of Xoc strain RS105, leading to the identification of two nitrilase enzyme family (NIT) genes, designated as AKO15524.1 and AKO15829.1, subsequently named NIT24 and NIT29, respectively. Our investigation unveiled that the deletion of NIT24 and NIT29 resulted in a notable reduction in IAA synthesis capacity within RS105, thereby impacting extracellular polysaccharide production. This deficiency was partially ameliorated through exogenous IAA supplementation. The study further substantiated that NIT24 and NIT29 have nitrilase activity and the ability to catalyse IAA production invitro. The lesion length and bacterial population statistics experiments confirmed that NIT24 and NIT29 positively regulated the pathogenicity of RS105, suggesting that NIT24 and NIT29 may regulate Xoc invasion by affecting IAA synthesis. Furthermore, our analysis corroborated mutant strains, RS105_ΔNIT24 and RS105_ΔNIT29, which elicited the outbreak of reactive oxygen species, the deposition of callose and the upregulation of defence-related gene expression in rice. IAA exerted a significant dampening effect on the immune responses incited by these mutant strains in rice. In addition, the absence of NIT24 and NIT29 affected the growth-promoting effect of Xoc on rice. This implies that Xoc may promote rice growth by secreting IAA, thus providing a more suitable microenvironment for its own colonization. In summary, our study provides compelling evidence for the existence of a nitrilase-dependent IAA biosynthesis pathway in Xoc. IAA synthesis-related genes promote Xoc colonization by inhibiting rice immune defence response and affecting rice growth by increasing IAA content in Xoc.

Effects of Azotobacter and Carbon Dioxide Concentrations on the Growth and Yield of Rice Plants Grown in Two Paddy Soils

Rice is an important staple crop influenced by rising CO2 and related climate change, but it is not well-known how N-fixing Azotobacter affects rice growth and yield under different CO2 concentrations. This study aimed to determine the effects of Azotobacter strains on the growth and yield of rice plants grown in two paddy soils under varying CO2 conditions. Rice plants inoculated with three Azotobacter strains were grown in a conventional rice soil (Dali) and an organic rice soil (Houlong) under 500 or 1000 ppm CO2. These three Azotobacter strains significantly increased the harvest index of rice plants grown in Dali soil under 1000 ppm CO2, but they did not significantly increase the harvest index for rice plants grown in Houlong soil under elevated CO2. Interestingly, only A. beijerinckii CHB 461 significantly promoted the thousand-grain weight of rice plants grown in both Dali and Houlong soils under elevated CO2. Dali soil had a high level of soil organic matter, exchangeable Ca and Mg, and available Cu and Zn, probably resulting in a better response of the rice plants to Azotobacter inoculation under elevated CO2. In conclusion, in the application of Azotobacter to promote rice growth and yield under future rising CO2 conditions, the soil properties and characteristics of Azotobacter strains may need to be considered.

Projecting the impact of climate change and elevated CO2 concentration on rice irrigation water requirement in China

Climate change and elevated CO2 concentrations significantly affect rice growth and water consumption. Understanding the specific impacts of climate change and elevated CO2 concentrations on rice physiological phenology, crop water demand (ETC), and irrigation water requirement (IR) is of great significance for the sustainable utilization of water resources and food security. This is particularly true in China, the world's largest rice producer. In this study, with the help of two rice phenological models, the modified Penman-Monteith equation, and the paddy water balance model, we project the changes in rice phenological period, ETC, and IR in four main rice-producing regions of China in the period 2015–2100 based on the 11 GCM outputs. The results show that the rice growing period is shortened in most rice-producing regions, except for the parts of the middle and lower reaches of the Yangtze River. Meanwhile, the trend of ETC and IR of rice varies slightly among regions in the future scenario, with almost all regions decreasing yearly except for the middle and lower reaches of the Yangtze River, where the trend is increasing. The progressively increasing atmospheric CO2 concentration has a “fertilization effect” on the crop, which can reduce the water requirements of rice. In the SSP585 scenario, the “ CO2 fertilization effect” can reduce up to 8.87 × 108 m3 of ETC and 6.94 × 108 m3 of IR in the middle and lower reaches of the Yangtze River in the period of 2090s. This study provides beneficial references to understand the response of rice ETC and IR to future climate change and CO2 concentration elevation in China and highlights that the simulation in terms of crop irrigation must account for the “CO2 fertilization effect”.