Heterosis, commonly referred to as hybrid vigor, describes the biological phenomenon by which F1 hybrids outperform their parents. The exploitation of rice heterosis has made a great contribution to yield improvements and global food security. However, a unified molecular theory explaining heterosis remains elusive. This review consolidates recent advances in rice heterosis research, focusing on genetic and multi-omics. We discuss the contribution of key genes, non-additive gene expression patterns, and metabolic changes that underpin hybrid performance. The genomic, transcriptomic, epigenetic, and metabolomic evidence supporting dominance, overdominance, and epistasis hypotheses for heterosis are highlighted and integrated. The collective evidence suggests that heterosis is not governed by a single universal mechanism but is a complex consequence of synergistic interactions from sequence variation to regulatory networks across multiple omics. We also highlight emerging applications of artificial intelligence (AI) driven prediction in the breeding of next-generation super-hybrid rice. We propose that key points of future heterosis research should extend beyond static omics snapshots to dynamic, developmental, and metabolic pathways related to yield formation, such as energy metabolism, which decode the ontogenetic basis and the mechanistic understanding of heterosis. Progress in this area will accelerate the breeding of high-yielding, resilient hybrid rice cultivars.

Understanding tolerance mechanisms and categorizing reliable physiochemical indicators related to their mechanisms is important for enhancing rapeseed tolerance and sustainable agricultural development. Putrescine (Put), one of the important polyamines, plays a promising role in promoting the synthesis of bioactive compounds related to plant development, especially under stress conditions. Herein, the potential role of Put in alleviating salt stress in rapeseed has been thoroughly investigated via priming application with different concentrations (0.1, 0.3, 0.5, 0.7, and 1 mM). Seed germination-related parameters and hormone-related genes were studied during seed imbibition under 150 mM of NaCl. Additionally, morpho-physiochemical characteristics, ionic content, and ion exchange-related genes were investigated in the shoots and roots of 7-day-old seedlings under salinity stress. Our results showed that Put-priming improved germination parameters by regulating seed germination and hormone-related genes under salinity stress, especially at 0.3 and 0.5 mM Put, compared with unprimed and hydroprimed (HP) seeds. Besides, it significantly enhanced seedling growth by preventing the degradation of photosynthetic pigments and modulating the proline and soluble solute accumulation in shoots and roots. Moreover, MDA, H2O2, and O2 contents decreased with Put-priming, especially at 0.5 mM, indicating the significant role of Put in ROS scavenging and inhibiting lipid peroxidation upon stress. Put-priming alleviated salt-induced oxidative stress by enhancing the structure and function of the enzymatic and non-enzymatic antioxidative systems, which protect the integrity of cellular membranes in seedlings under stress conditions. Our study observed increased Na+ and decreased K+ contents under salt treatments versus control (Ctrl), whereas Put treatments not only reduced Na+ but also increased K+ accumulation, lowering the Na+/K+ ratio, especially at 0.3 and 0.5 mM Put versus unprimed and HP seedlings. Put-priming showed strikingly stronger effects on intracellular Na+ and K+ homeostasis by regulating ion exchange-related genes, which upregulated the gene expression of BnH+-ATPase, BnNHX6, BnSOS1, BnSKOR, BnHKT1, and BnHKT8 that modulated Na+ influx and K+ efflux under salinity stress. Our results provide an integrative understanding and scientific basis for the exogenous application of Put as a promising method for improving salt tolerance in rapeseed seedlings at morpho-physiochemical and molecular levels, which provides a convenient, fast, and environmentally friendly strategy to help crops adapt to be used for cultivation in saline soil.

The formation of rice aroma is a complex process that is influenced by genetic and environmental factors. More than 500 fragrance compounds have been documented in fragrant rice, among which 2-AP dominates the aroma of rice. This paper introduced the identification of OsBadh2 in the biosynthesis of 2-AP in rice. Then, non-enzymatic and enzymatic pathways of the 2-AP biosynthesis have been comprehensively investigated. In detail, 2-AP biosynthesis-associated enzyme, such as OsBADH2, OsP5CS, OsGAD, OsGAPDH, OsProDH, OsOAT, OsODC and OsDAO, have been summarized, while MG and fatty acids are also implicated in modulating the biosynthesis of 2-AP by providing the acetyl groups. Moreover, extensive collections of traditional fragrant rice varieties have been collated, together with the OsBadh2 haplotypes of 312 fragrant rice germplasm in China. And finally, genetic engineering of OsBadh2 and other genes in the 2-AP biosynthesis to develop fragrant rice are discussed.

Rice (Oryza sativa L.) is a chilling-sensitive staple food crop, and thus, low temperature significantly affects rice growth and yield. Many studies have focused on the cold shock of rice although chilling acclimation is more likely to happen in the field. In this paper, a genome-wide association study (GWAS) was used to identify the genes that participated in cold stress and chilling accumulation. A total of 235 significantly associated single-nucleotide polymorphisms (SNPs) were identified. Among them, we detected 120 and 88 SNPs for the relative shoot fresh weight under cold stress and chilling acclimation, respectively. Furthermore, 11 and 12 quantitative trait loci (QTLs) were identified for cold stress and chilling acclimation, respectively, by integrating the co-localized SNPs. Interestingly, we identified 10 and 15 candidate genes in 11 and 12 QTLs involved in cold stress and chilling acclimation, respectively, and two new candidate genes (LOC_Os01g62410, LOC_Os12g24490) were obviously up-regulated under chilling acclimation. Furthermore, OsMYB3R-2 (LOC_Os01g62410) that encodes a R1R2R3 MYB gene was associated with cold tolerance, while a new C3HC4-type zinc finger protein-encoding gene LOC_Os12g24490 was found to function as a putative E3 ubiquitin-protein ligase in rice. Moreover, haplotype, distribution, and Wright’s fixation index (FST) of both genes showed that haplotype 3 of LOC_Os12g24490 is more stable in chilling acclimation, and the SNP (A > T) showed a difference in latitudinal distribution. FST analysis of SNPs in OsMYB3R-2 (LOC_Os01g62410) and LOC_Os12g24490 indicated that several SNPs were under selection in rice indica and japonica subspecies. This study provided new candidate genes in genetic improvement of chilling acclimation response in rice.

MAIN CONCLUSION:Associated analysis of GWAS with RNA-seq had detected candidate genes responsible for cold stress and chilling acclimation in rice. Haplotypes of two candidate genes and geographic distribution were analyzed. To explore new candidate genes and genetic resources for cold tolerance improvement in rice, genome-wide association study (GWAS) mapping experiments with 351 rice core germplasms was performed for three traits (survival rate, shoot length and chlorophyll content) under three temperature conditions (normal temperature, cold stress and chilling acclimation), yielding a total of 134 QTLs, of which 54, 59 and 21 QTLs were responsible for normal temperature, cold stress and chilling acclimation conditions, respectively. Integrated analysis of significant SNPs in 134 QTLs further identified 116 QTLs for three temperature treatments, 53, 43 and 18 QTLs responsible for normal temperature, cold stress and chilling acclimation, respectively, and 2 QTLs were responsible for both cold stress and chilling acclimation. Matching differentially expressed genes from RNA-seq to 43 and 18 QTLs for cold stress and chilling acclimation, we identified 69 and 44 trait-associated candidate genes, respectively, to be classified into six and five groups, particularly involved in metabolisms, reactive oxygen species scavenging and hormone signaling. Interestingly, two candidate genes LOC_Os01g04814, encoding a vacuolar protein sorting-associating protein 4B, and LOC_Os01g48440, encoding glycosyltransferase family 43 protein, showed the highest expression levels under chilling acclimation. Haplotype analysis revealed that both genes had a distinctive differentiation with subpopulation. Haplotypes of both genes with more japonica accessions have higher latitude distribution and higher chilling tolerance than the chilling sensitive indica accessions. These findings reveal the new insight into the molecular mechanism and candidate genes for cold stress and chilling acclimation in rice.

In recent years, much attention has been directed toward using nanoparticles (NPs) as one of the most effective strategies to improve plant growth, especially under salt stress conditions. Further research has been conducted to develop NPs using various chemical ways; accordingly, knowledge about the beneficial effect of bioSeNPs in rapeseed is obscure. Selenium (Se) is a vital micronutrient with a series of physiological and antioxidative properties. Seed priming is emerging as a low-cost, efficient, and environment-friendly seed treatment in nanotechnology. The current study was carried out to examine the promising effects of nanopriming via bioSeNPs on the expression level of aquaporin genes, seed microstructure, seed germination, growth traits, physiochemical attributes, and minerals uptake of two rapeseed cultivars under salinity stress conditions. Our investigation monitored the positive effects of bioSeNPs on the expression level of aquaporin genes (BnPIP1-1 and BnPIP2-1) and water uptake during the seed imbibition (4 and 8 h of priming), which indicated higher imbibition potential and germination promotion with bioSeNPs application (most effective at 150 μmol/L). The total performance index was significantly enhanced with nano-treatments in rapeseed seedlings. Collectively, nano-application improved seed microstructure, seed germination, and photosynthetic efficiency directly correlated with higher seedlings biomass, especially with a higher concentration of bioSeNPs. The enhancement in α-amylase and free amino acid contents in nanoprimed seeds resulted in rapid seed germination. Moreover, bioSeNPs increased the osmotic adjustment and enhanced the efficiency of the plant's defense system by improving the activity of enzymatic and non-enzymatic antioxidants, thus enhancing ROS scavenging under salt stress. The obtained results may indicate the strengthening of seed vigor, improving seedling growth and physiochemical attributes via bioSeNPs. Our findings displayed that bioSeNPs modulated the Na+ and K+ uptake, which improved the rapeseed growth and showed a close relationship with the low contents of toxic Na+ ion; thus, it prevented oxidative damage due to salt stress. This comprehensive data can add more knowledge to understand the mechanisms behind plant-bioSeNPs interaction and provide physiological evidence for the beneficial roles of nanopriming using bioSeNPs on rapeseed germination and seedling development under salinity stress conditions. Such studies can be used to develop simple prepackaged nano primer products, which can be used before sowing to boost seed germination and crop productivity under stress conditions.

Measuring metabolite patterns and antioxidant ability is vital to understanding the physiological and molecular responses of plants under salinity. A morphological analysis of five rapeseed cultivars showed that Yangyou 9 and Zhongshuang 11 were the most salt-tolerant and -sensitive, respectively. In Yangyou 9, the reactive oxygen species (ROS) level and malondialdehyde (MDA) content were minimized by the activation of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) for scavenging of over-accumulated ROS under salinity stress. Furthermore, Yangyou 9 showed a significantly higher positive correlation with photosynthetic pigments, osmolyte accumulation, and an adjusted Na+/K+ ratio to improve salt tolerance compared to Zhongshuang 11. Out of 332 compounds identified in the metabolic profile, 225 metabolites were filtrated according to p < 0.05, and 47 metabolites responded to salt stress within tolerant and sensitive cultivars during the studied time, whereas 16 and 9 metabolic compounds accumulated during 12 and 24 h, respectively, in Yangyou 9 after being sown in salt treatment, including fatty acids, amino acids, and flavonoids. These metabolites are relevant to metabolic pathways (amino acid, sucrose, flavonoid metabolism, and tricarboxylic acid cycle (TCA), which accumulated as a response to salinity stress. Thus, Yangyou 9, as a tolerant cultivar, showed improved antioxidant enzyme activity and higher metabolite accumulation, which enhances its tolerance against salinity. This work aids in elucidating the essential cellular metabolic changes in response to salt stress in rapeseed cultivars during seed germination. Meanwhile, the identified metabolites can act as biomarkers to characterize plant performance in breeding programs under salt stress. This comprehensive study of the metabolomics and antioxidant activities of Brassica napus L. during the early seedling stage is of great reference value for plant breeders to develop salt-tolerant rapeseed cultivars.

Salinity stress negatively affects the plant's developmental stages through micronutrient imbalance. As an essential micronutrient, ZnO can substitute Na+ absorption under saline conditions. Therefore, nanoparticles as technological innovation, improve the plant growth efficiency under biotic and abiotic stresses. Nano-priming has become widely applicable in agricultural research during the last decade. The current study was conducted to highlight the impact of ZnONPs priming on seedling biological processes under 150 mM of NaCl using two rapeseed cultivars during the early seedling stage. All concentrations of ZnONPs increased the germination parameters i.e., FG%, GR, VI (I), and VI (II). Meanwhile, the high concentration (ZnO 100%) showed the highest increase in shoot length (9.60% and 25.63%), root length (41.64% and 48.17%) for Yang You 9 and Zhong Shuang 11 over hydro-priming, respectively, as well as biomass. Additionally, nano-priming improved the proline, soluble sugar, and soluble protein contents as a result of osmotic protection modulation. Moreover, nano-priming alleviated ROS and biosynthesis pigments through the reduction of accumulated (H2O2) and (O-2(-)), and chlorophyll degradation, respectively, also enhanced antioxidant adjustment via improving the plant defense system. Nano-priming substituted the Na+ by Zn2+, K+, and Ca2+, and compensated the deficit of micronutrients, thus reduced the Na+ toxicity in the cell cytosol. To track the effects of priming during seed imbibition, it noticed that ZnO 100% and ZnO 100%+S increased the Linoleic and Linolenic acids among the studied fatty acids composition by 12.02%, 7.59%, 13.27%, and 10.38% (Yang You 9), 7.42%, 2.77%, 2.93%, and 1.49% (Zhong Shuang 11) over the hydro-priming, respectively. Moreover, the gene expression patterns of BnCAM and BnPER reflected the enhancement of germination levels, notably under the influence of ZnO 100% priming, which increased the level of BnCAM by 70.42% and 111.9% in Yang You 9 and Zhong Shuang 11, respectively. Consequently, ZnO nano-priming enhanced the seedling development through the biosynthesis of pigments, osmotic protection, reduction of ROS accumulation, adjustment of antioxidant enzymes, and improvement of the nutrient absorption, thus enhancing the economic yield under saline conditions.

Fibrillins (FBNs) constitute a plastid-lipid-associated protein family that plays a role in chloroplast development, lipids metabolism and stress responses in plants. Until now, FBNs have been functionally characterized in stability of thylakoid and responses to the different stress stimuli. Consequently, phylogeny, domain composition and structural features of 121 FBNs family proteins from ten representative species have been identified. As results, phylogenetic analysis demonstrated that FBNs proteins were grouped into 24 clades and further subdivided into three groups, including terrestrial plant-specific, algae-specific, and intermediate group. These FBNs genes had different numbers of introns and exons but encoded the conserved N-terminal chloroplast transport peptide (CTP) domains and plastid lipid-associated protein (PAP) domains, which greatly contributed to the sub-functionalization and neo-functionalization. Meanwhile, the CTP domains of eleven OsFBN proteins except OsFBN8 could help them transport into chloroplasts. The PAP domains of OsFBN2 and OsFBN4 showed the in vitro specific binding activity to C12-C22 fatty acids that were affected by YxD motif. The qRT-PCR analysis showed that OsFBN genes were differentially induced by heat stress and cold stress in rice. Collectively, this study has provided the new insights into the evolution, structure, and functions of FBN gene family and will help to elucidate the molecular mechanisms of these proteins functioning in growth, development and adaptations in the global climate change.