OsKEAP1 Interacts with OsABI5 and Its Downregulation Increases the Transcription of OsABI5 and the ABA Response Genes in Germinating Rice Seeds

Genome-Wide Identification and Expression Analysis of Thionin Family in Rice (Oryza sativa) and Functional Characterization of OsTHION15 in Drought Stress and ABA Stress

The OsTHION family represents a class of cysteine-rich signal peptides widely recognized for their significant roles in plant disease resistance and immunity. While members of this family are known to be induced under various biotic and abiotic stresses, their responses to environmental stressors beyond disease resistance remain underexplored. This study investigates the evolution, expression patterns, and functional roles of the OsTHION gene family in rice (Oryza sativa) under diverse stress conditions. Using sequence data from the Phytozome database, we identified 44 OsTHION family members and classified them into four groups based on phylogenetic analysis. Cis-acting element analysis revealed that the promoter regions of OsTHION genes are enriched with regulatory elements associated with light response, hormone signaling, plant growth, and stress responses. The OsTHION genes exhibit complex organ-specific expression patterns, with OsTHION30 and OsTHION36 showing ubiquitous expression, while other members are highly expressed in specific tissues or developmental stages. Under drought, salt, and low-temperature stress, OsTHION genes undergo significant expression changes, underscoring their critical role in plant adaptation to environmental challenges. Notably, OsTHION15 was markedly upregulated under drought stress, and the Osthion15 mutant displayed heightened sensitivity to drought and ABA stress, confirming its pivotal role in stress resistance. RNA sequencing analysis identified many differentially expressed genes (DEGs), primarily enriched in pathways related to ribosomal function and plant hormone signaling, suggesting that OsTHION15 may regulate stress responses through multiple mechanisms. In summary, this study advances our understanding of the OsTHION gene family and highlights its intricate involvement in regulating rice growth, development, and environmental stress responses. These findings offer valuable insights and technical support for crop improvement, with potential applications in enhancing environmental adaptability and yield stability in crops.

A rice transcription factor, OsMADS57, positively regulates high salinity tolerance in transgenic Arabidopsis thaliana and Oryza sativa plants

MADS-box transcription factors (TFs) play indispensable roles in various aspects of plant growth, development as well as in response to environmental stresses. Several MADS-box genes have been reported to be involved in the salt tolerance in different plant species. However, the role of the transcription factor OsMADS57 under salinity stress is still unknown. Here, the results of this study showed that OsMADS57 was mainly expressed in roots and leaves of rice plants (Oryza sativa). Gene expression pattern analysis revealed that OsMADS57 was induced by NaCl. Overexpression of OsMADS57 in both Arabidopsis thaliana (A. thaliana) and rice could improve their salt tolerance, which was demonstrated by higher germination rates, longer root length and better growth status of overexpression plants than wild type (WT) under salinity conditions. In contrast, RNA interference (RNAi) lines of rice showed more sensitivity towards salinity. Moreover, less reactive oxygen species (ROS) accumulated in OsMADS57 overexpressing lines when exposed to salt stress, as measured by 3, 3'-diaminobenzidine (DAB) or nitroblue tetrazolium (NBT) staining. Further experiments exhibited that overexpression of OsMADS57 in rice significantly increased the tolerance ability of plants to oxidative damage under salt stress, mainly by increasing the activities of antioxidative enzymes such as superoxide dismutase (SOD) and peroxidase (POD), reducing malonaldehyde (MDA) content and improving the expression of stress-related genes. Taken together, these results demonstrated that OsMADS57 plays a positive role in enhancing salt tolerance by activating the antioxidant system.

Melatonin Alleviates Low-Temperature Stress via ABI5-Mediated Signals During Seed Germination in Rice (Oryza sativa L.)

With increasing areas of direct sowing, low-temperature (LT) stress drastically affects global rice production. Exogenous applications of melatonin (MT) serve as one of the effective ways to improve seed germination under various stress conditions. In this study, we found that MT treatment greatly improved the LT stress-induced loss of germination percentage and the weak performance of seedlings under LT of constant 20°C (LT20). This was largely dependent on the activated antioxidant system and enhanced activities of storage substance utilization-associated enzymes. Moreover, we also detected that exogenous feeding of MT significantly increased the biosynthesis of gibberellin (GA) and endogenous MT but simultaneously inhibited the accumulation of abscisic acid (ABA) and hydrogen peroxide (H2O2) under LT20 stress. These results suggested that MT had antagonistic effects on ABA and H2O2. In addition, MT treatment also significantly enhanced the expression of CATALYSE 2 (OsCAT2), which was directly regulated by ABA-INSENSITIVE 5 (OsABI5), a core module of ABA-stressed signals, and thus promoting the H2O2 scavenging to reach reactive oxygen species (ROS) homeostasis, which consequently increased GA biosynthesis. However, in abi5 mutants, OsCAT2 failed in response to LT20 stress irrespective of MT treatment, indicating that OsABI5 is essential for MT-mediated seed germination under LT20 stress. Collectively, we now demonstrated that MT showed a synergistic interaction with an ABI5-mediated signal to mediate seed germination, partially through the direct regulation of OsCAT2.

Updates on the Role of ABSCISIC ACID INSENSITIVE 5 (ABI5) and ABSCISIC ACID-RESPONSIVE ELEMENT BINDING FACTORs (ABFs) in ABA Signaling in Different Developmental Stages in Plants

The core abscisic acid (ABA) signaling pathway consists of receptors, phosphatases, kinases and transcription factors, among them ABA INSENSITIVE 5 (ABI5) and ABRE BINDING FACTORs/ABRE-BINDING PROTEINs (ABFs/AREBs), which belong to the BASIC LEUCINE ZIPPER (bZIP) family and control expression of stress-responsive genes. ABI5 is mostly active in seeds and prevents germination and post-germinative growth under unfavorable conditions. The activity of ABI5 is controlled at transcriptional and protein levels, depending on numerous regulators, including components of other phytohormonal pathways. ABFs/AREBs act redundantly in regulating genes that control physiological processes in response to stress during vegetative growth. In this review, we focus on recent reports regarding ABI5 and ABFs/AREBs functions during abiotic stress responses, which seem to be partially overlapping and not restricted to one developmental stage in Arabidopsis and other species. Moreover, we point out that ABI5 and ABFs/AREBs play a crucial role in the core ABA pathway’s feedback regulation. In this review, we also discuss increased stress tolerance of transgenic plants overexpressing genes encoding ABA-dependent bZIPs. Taken together, we show that ABI5 and ABFs/AREBs are crucial ABA-dependent transcription factors regulating processes essential for plant adaptation to stress at different developmental stages.