Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major threat to global rice productivity. Although hybrid rice breeding has significantly enhanced yields, persistent genetic vulnerabilities within restorer lines continue to compromise BB resistance. This study addresses this challenge by implementing functional marker-assisted selection (FMAS) to pyramid two broad-spectrum resistance (R) genes, Xa21 and Xa23, into the elite, yet BB-susceptible, restorer line K608R. To enable precise Xa23 genotyping, we developed a novel three-primer functional marker (FM) system (IB23/CB23/IR23). This system complements the established U1/I2 markers used for Xa21. This recombination-independent FMAS platform facilitates simultaneous, high-precision tracking of both homozygous and heterozygous alleles, thereby effectively circumventing the linkage drag limitations typical of conventional markers. Through six generations of marker-assisted backcrossing followed by intercrossing, we generated K608R2123 pyramided lines harboring both R genes in homozygous states, achieving a recurrent parent genome recovery rate of 96.93%, as determined by single nucleotide polymorphism (SNP) chip analysis. The pyramided lines exhibited enhanced resistance against six virulent Xoo pathogenic races while retaining parental yield performance across key agronomic traits. Our FMAS strategy overcomes the historical trade-off between broad-spectrum resistance and the preservation of elite phenotypes, with the developed lines exhibiting resistance coverage complementary to that of both introgressed R genes. This integrated approach provides breeders with a reliable molecular tool to accelerate the development of high-yielding, disease-resistant varieties, demonstrating significant potential for practical deployment in rice improvement programs. The K608R2123 germplasm represents a dual-purpose resource suitable for both commercial hybrid seed production and marker-assisted breeding programs, and it confers synergistic resistance against diverse Xoo races, thereby providing a pivotal breeding resource for sustainable BB control in epidemic regions.

Exogenous melatonin has emerged as a pivotal multifunctional signaling molecule, recognized for its critical role in enhancing stress tolerance and improving crop productivity. N6‐methyladenosine (m6A) is the most prevalent internal modification found in eukaryotic mRNA and plays a crucial role in regulating plant growth, development, and stress responses. Despite its importance, the regulatory mechanisms of the m6A pathway in rice exposed to exogenous melatonin remain inadequately investigated. This study investigates systematic analysis of m6A‐regulatory gene families in rice. We identified a total of 124 genes, which include 7 writers, 22 readers, and 95 erasers. The distribution of these genes is uneven across the 11 chromosomes of the rice genome. Analysis of conserved domains revealed structural signatures that are specific to each gene family. Phylogenetic relationships with dicot and monocot species offered insights into evolutionary trajectories. Notably, gene structure and motif analyses revealed functional divergence within and between gene families. Cis‐element analysis identified abundance motifs associated with stress adaptation, hormonal signaling, and TFs, including ABRE, DRE, and MYB. Furthermore, synteny analysis unveiled both conserved regions and lineage‐specific expansions, particularly within the YTH and ALKBH families. The protein interaction network revealed robust connections among subgroups and identified 10 hub genes. GO and KEGG analyses indicated significant enrichment in stress‐related pathways, including secondary metabolite biosynthesis, flavonoid biosynthesis, and cysteine and methionine metabolism. RT‐qPCR validates that melatonin Osm6As significantly influences the expression of targeted genes, with melatonin upregulations exhibiting a time‐dependent pattern. Furthermore, GFP tagging of OsECT2 revealed that protoplasts are evenly distributed, suggesting robust nuclear enrichment of fluorescence. This study offers new insights into the epitranscriptomic regulatory responses of the m6A‐modifier.

Melatonin (MT) can enhance plant stress tolerance by activating the internal defense system, but its application in rubber trees has been barely reported up to now. In this study, we found that the relative electrical conductivity (REC), H₂O₂, and malondialdehyde (MDA) contents were significantly higher in the leaves of rubber tree seedlings under drought stress compared to the control (water treatment), whereas chlorophyll contents were obviously lower in the leaves under drought stress compared to the control. MT partly relieves the aforementioned drought-induced adverse effects by dramatically reducing chlorophyll degradation, H₂O₂ accumulation, MDA content, and REC. Comparative transcriptomes among the PEG (P), MT (M), and PEG + MT (PM) treatments against the control showed that 213, 896, and 944 genes were differently expressed in rubber tree seedlings treated with M, P, and PM in contrast to the control. Among the 64 differently expressed genes (DEGs) being common among the three comparisons, the expression profiles of 25 were opposite in MH compared with PH. Intriguingly, all the KEGG pathways of the DEGs mentioned above belonged to metabolism including energy metabolism, carbohydrate metabolism, amino acid metabolism, and the metabolism of cofactors and vitamins. Exogenous application of MT mainly regulated the genes associated with photosynthesis and the anti-oxidative defense system, thereby enhancing the antioxidant protection of rubber tree seedlings under drought stress. These results suggest that exogenous melatonin application can effectively enhance drought tolerance by heightening ROS scavenging to decrease H₂O₂ accumulation in rubber tree seedlings. Our results elucidate the molecular mechanisms of MT’s roles in drought stress, which help to employ exogenous MT to boost drought tolerance in the rubber tree.

Small heat shock proteins (sHSPs) are involved in a wide range of abiotic stresses, yet the functional roles of sHSP family genes in rubber tree salt tolerance remain largely uncharacterized. In this study, HbsHSP23.8a, a novel sHSP gene from rubber tree, was cloned and analyzed in detail. HbsHSP23.8a consists of a targeting peptide, an N-terminal domain, an α-crystallin domain (ACD), and C-terminal extensions. Additionally, putative dimer interface and conserved amino acid sequences were identified in the ACD and N-terminal domain of HbsHSP23.8a, respectively. HbsHSP23.8a transcripts were detected in different tissues and developmental stages of leaves, indicating that HbsHSP23.8a was associated with rubber tree growth and development. Besides tapping panel dryness (TPD), HbsHSP23.8a was also involved in low-temperature, high-salt, methyl jasmonate (MeJA), and ethephon (ET) responses. Under salt stress, overexpression of HbsHSP23.8a in transgenic tobacco plants exhibited greater plant height and fresh weight than wild-type (WT) plants. In addition, tobacco plants overexpressing HbsHSP23.8a increased the activities of antioxidant enzymes and decreased hydrogen peroxide (H₂O₂) accumulation and chlorophyll degradation under salt stress compared with the WT plants. Collectively, our results suggest that HbsHSP23.8a is related to rubber tree growth, TPD, leaf development, stress and hormone responses. Furthermore, heterologous expression of HbsHSP23.8a is associated with enhanced salt tolerance in transgenic tobacco, which may be attributed to elevated antioxidant enzyme activities, reduced cellular H₂O₂ accumulation, and alleviated chlorophyll degradation.