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Nostoc flagelliforme is a terrestrial cyanobacterium that can resist many types of stressors, including drought, ultraviolet radiation, and extreme temperatures. In this study, we identified the drought tolerance gene NfcrtO, which encodes a β-carotene ketolase, through screening the transcriptome of N. flagelliforme under water loss stress. Prokaryotic expression of NfcrtO under 0.6 mol/L sorbitol or under 0.3 mol/L NaCl stress significantly increased the growth rate of Escherichia coli. When NfcrtO was heterologously expressed in rice, the seedling height and root length of NfcrtO-overexpressing rice plants were significantly higher than those of the wild type (WT) plants grown on ½ Murashige and Skoog solid medium with 120 mmol/L mannitol at the seedling stage. Transcriptome analysis revealed that NfcrtO was involved in osmotic stress, antioxidant, and other stress-related pathways. Additionally, the survival rate of the NfcrtO-overexpression lines was significantly higher than that of the WT line under both hydroponic stress (24% PEG and 100 mmol/L H2O2) and soil drought treatment at the seedling stage. Physiological traits, including the activity levels of superoxide dismutase, peroxidase, catalase, total antioxidant capacity, and the contents of proline, trehalose, and soluble sugar, were significantly improved in the NfcrtO-overexpression lines relative to those in the WT line under 20% PEG treatment. Furthermore, when water was withheld at the booting stage, the grain yield per plant of NfcrtO-overexpression lines was significantly higher than that of the WT line. Yeast two-hybrid analysis identified interactions between NfcrtO and Dna J protein, E3 ubiquitin-protein ligase, and pyrophosphate-energized vacuolar membrane proton pump. Thus, heterologous expression of NfcrtO in rice could significantly improve the tolerance of rice to osmotic stress, potentially facilitating the development of new rice varieties.

Summary: Pollen germination and pollen tube growth are important physiological processes of sexual reproduction of plants and also are involved in signal transduction. Our previous study reveals that ZmSTK1 and ZmSTK2 are two receptor‐like cytoplasmic kinases (RLCK) homologs in Zea mays as members of receptor‐like protein kinase (RLK) subfamily, sharing 86% identity at the amino acid level. Here, we report that ZmSTK1 and ZmSTK2, expressed at late stages of pollen development, regulate maize pollen development with additive effect. ZmSTK1 or ZmSTK2 mutation exhibited severe pollen transmission deficiency, which thus influenced pollen fertility. Moreover, the kinase domains of ZmSTKs were cross‐interacted with C‐terminus of enolases detected by co‐immunoprecipitation (Co‐IP) and yeast two‐hybrid system (Y2H), respectively. Further, the detective ZmSTK1 or ZmSTK2 was associated with decreased activity of enolases and also reduced downstream metabolite contents, which enolases are involved in glycolytic pathway, such as phosphoenolpyruvate (PEP), pyruvate, ADP/ATP, starch, glucose, sucrose and fructose. This study reveals that ZmSTK1 and ZmSTK2 regulate maize pollen development and indirectly participate in glycolytic pathway. [ABSTRACT FROM AUTHOR]