Identification of the OsCML4 Gene in Rice Related to Salt Stress Using QTL Analysis

Gamma-aminobutyric acid treatment promotes resistance against Sogatella furcifera in rice

The Sogatella furcifera (Horváth) (Homoptera: Delphacidae) is a white-backed planthopper (WBPH) that causes "hopper burn" in rice, resulting in severe yield loss. Gamma-aminobutyric acid (GABA) is a well-known neurotransmitter that inhibits neurotransmission in insects by binding to specific receptors. In this study, we investigated the potential role of GABA in modulating rice resistance to WBPH and evaluated possible defense mechanisms. The experiment was conducted in green house in pots consist of four groups: control, GABA-treated, WBPH-infested, and WBPH-infested treated with GABA. Among the various tested concentration of GABA, 15 mM GABA was applied as a single treatment in water. The treatment was administered one week before WBPH infestation. The results revealed that 15 mM GABA treatment strongly increased WBPH resistance. A plate-based assay indicated that direct application of 15 mM GABA increased the mortality rate of WBPH and increased the damage recovery rate in rice plants. We found that GABA treatment increased the activation of antioxidant enzymes and reduced the reactive oxygen species content and malondialdehyde contents, and reduced the damage rate caused by WBPH. Interestingly, GABA-supplemented plants infested with WBPH exhibited increased phenylalanine ammonia-lyase and pathogenesis-related (PR) genes expression levels. GABA induced the accumulation of abscisic acid (ABA) and salicylic acid (SA) and enhanced the stomata closure and reduced leaf vessels to reduce water conductance during WBPH stress. Furthermore, we found that GABA application to the plant induced the expression of Jasmonic acid (JA) biosynthesis genes (LOX, AOS, AOC, and OPR) and melatonin biosynthesis-related genes (TDC, T5H, ASMT, and SNAT). Our study suggested that GABA increases resistance against WBPH infestation by regulating antioxidant defense system, TCA cycle regulation, phytohormonal signaling, and PR gene regulation.

CALMODULIN-LIKE16 and PIN-LIKES7a cooperatively regulate rice seedling primary root elongation under chilling

Low-temperature sensitivity at the germination stage is a challenge for direct seeding of rice in Asian countries. How Ca2+ and auxin (IAA) signaling regulate primary root growth under chilling remains unexplored. Here, we showed that OsCML16 interacted specifically with OsPILS7a to improve primary root elongation of early rice seedlings under chilling. OsCML16, a subgroup 6c member of the OsCML family, interacted with multiple cytosolic loop regions of OsPILS7a in a Ca2+-dependent manner. OsPILS7a localized to the endoplasmic reticulum membranes and functioned as an auxin efflux carrier in a yeast growth assay. Transgenics showed that presence of OsCML16 enhanced primary root elongation under chilling, whereas the ospils7a knockout mutant lines showed the opposite phenotype. Moreover, under chilling conditions, OsCML16 and OsPILS7a-mediated Ca2+ and IAA signaling and regulated the transcription of IAA signaling-associated genes (OsIAA11, OsIAA23, and OsARF16) and cell division marker genes (OsRAN1, OsRAN2, and OsLTG1) in primary roots. These results show that OsCML16 and OsPILS7a cooperatively regulate primary root elongation of early rice seedlings under chilling. These findings enhance our understanding of the crosstalk between Ca2+ and IAA signaling and reveal insights into the mechanisms underlying cold-stress response during rice germination.

Joint QTL Mapping and Transcriptome Sequencing Analysis Reveal Candidate Genes for Salinity Tolerance in Oryza sativa L. ssp. Japonica Seedlings

Salinity stress is one of the major abiotic stresses affecting crop growth and production. Rice is an important food crop in the world, but also a salt-sensitive crop, and the rice seedling stage is the most sensitive to salt stress, which directly affects the final yield formation. In this study, two RIL populations derived from the crosses of CD (salt-sensitive)/WD (salt-tolerant) and KY131 (salt-sensitive)/XBJZ (salt-tolerant) were used as experimental materials, and the score of salinity toxicity (SST), the relative shoot length (RSL), the relative shoot fresh weight (RSFW), and the relative shoot dry weight (RSDW) were used for evaluating the degree of tolerance under salt stress in different lines. The genetic linkage map containing 978 and 527 bin markers were constructed in two RIL populations. A total of 14 QTLs were detected on chromosomes 1, 2, 3, 4, 7, 9, 10, 11, and 12. Among them, qSST12-1, qSST12-2, and qRSL12 were co-localized in a 140-kb overlap interval on chromosome 12, which containing 16 candidate genes. Furthermore, transcriptome sequencing and qRT-PCR were analyzed in CD and WD under normal and 120 mM NaCl stress. LOC_Os12g29330, LOC_Os12g29350, LOC_Os12g29390, and LOC_Os12g29400 were significantly induced by salt stress in both CD and WD. Sequence analysis showed that LOC_Os12g29400 in the salt-sensitive parents CD and KY131 was consistent with the reference sequence (Nipponbare), whereas the salt-tolerant parents WD and XBJZ differed significantly from the reference sequence both in the promoter and exon regions. The salt-tolerant phenotype was identified by using two T3 homozygous mutant plants of LOC_Os12g29400; the results showed that the score of salinity toxicity (SST) of the mutant plants (CR-3 and CR-5) was significantly lower than that of the wild type, and the seedling survival rate (SSR) was significantly higher than that of the wild type, which indicated that LOC_Os12g29400 could negatively regulate the salinity tolerance of rice at the seedling stage. The results lay a foundation for the analysis of the molecular mechanism of rice salinity tolerance and the cultivation of new rice varieties.

Halotolerant endophytic bacteria alleviate salinity stress in rice (oryza sativa L.) by modulating ion content, endogenous hormones, the antioxidant system and gene expression

Excessive salinity reduces crop production and negatively impacts agriculture worldwide. We previously isolated endophytic bacterial strains from two halophytic species: Artemisia princeps and Chenopodium ficifolium. We used three bacterial isolates: ART-1 (Lysinibacillus fusiformis), ART-10 (Lysinibacillus sphaericus), and CAL-8 (Brevibacterium pityocampae) to alleviate the impact of salinity stress on rice. The impact of 160 mM NaCl salinity on rice was significantly mitigated following inoculation with these bacterial strains, resulting in increased growth and chlorophyll content. Furthermore, OsNHX1, OsAPX1, OsPIN1 and OsCATA expression was increased, but OsSOS expression was decreased. Inductively coupled plasma mass spectrometry (ICP-MS) revealed reduced K+ and Na+ levels in shoots of bacteria-inoculated plants, whereas that of Mg2+ was increased. Bacterial inoculation reduced the content of total flavonoids in rice leaves. Salinized plants inoculated with bacteria showed reduced levels of endogenous salicylic acid (SA) and abscisic acid (ABA) but increased levels of jasmonic acid (JA). In conclusion, the bacterial isolates ART-1, ART-10, and CAL-8 alleviated the adverse effect of salinity on rice growth, which justifies their use as an eco-friendly agricultural practice.

Drought-triggered leaf transcriptional responses disclose key molecular pathways underlying leaf water use efficiency in sugarcane (Saccharum spp.)

Drought is a major constraint to sugarcane (Saccharum spp.) production and improving the water use efficiency (WUE) is a critical trait for the sustainability of this bioenergy crop. The molecular mechanism underlying WUE remains underexplored in sugarcane. Here, we investigated the drought-triggered physiological and transcriptional responses of two sugarcane cultivars contrasting for drought tolerance, 'IACSP97-7065' (sensitive) and 'IACSP94-2094' (tolerant). After 21 days without irrigation (DWI), only 'IACSP94-2094' exhibited superior WUE and instantaneous carboxylation efficiency, with the net CO₂ assimilation being less impacted when compared with 'IACSP97-7065'. RNA-seq of sugarcane leaves at 21 DWI revealed a total of 1,585 differentially expressed genes (DEGs) for both genotypes, among which 'IACSP94-2094' showed 617 (38.9%) exclusive transcripts (212 up- and 405 down-regulated). Functional enrichment analyses of these unique DEGs revealed several relevant biological processes, such as photosynthesis, transcription factors, signal transduction, solute transport, and redox homeostasis. The better drought-responsiveness of 'IACSP94-2094' suggested signaling cascades that foster transcriptional regulation of genes implicated in the Calvin cycle and transport of water and carbon dioxide, which are expected to support the high WUE and carboxylation efficiency observed for this genotype under water deficit. Moreover, the robust antioxidant system of the drought-tolerant genotype might serve as a molecular shield against the drought-associated overproduction of reactive oxygen species. This study provides relevant data that may be used to develop novel strategies for sugarcane breeding programs and to understand the genetic basis of drought tolerance and WUE improvement of sugarcane.

Growth or survival: What is the role of calmodulin-like proteins in plant?

Calcium signalling, including pulse, amplitude, and duration, is essential for plant development and response to various stimuli. However, the calcium signalling should be decoded and translated by calcium sensors. In plants, three classes of calcium-binding proteins have been identified as calcium sensors, including calcium-dependent protein kinase (CDPK), calcineurin B-like protein (CBL), and calmodulin (CaM). Calmodulin-like proteins (CMLs), which have several EF-hands, also serve as specific calcium sensors and can sense, bind, and interpret the calcium signal during the plant's growth and defense decision-making processes. In recent decades, the function of CMLs in plant development and response to various stimuli has been systematically reviewed, shedding light on the molecular mechanism of plant CML-mediated networks in calcium signal transduction. Here, by providing an overview of CML expression and biological function in plants, we demonstrate that growth-defense trade-offs occur during calcium sensing, an aspect that has not been well studied in recent years.