The impact of drought stress on plant growth in arid regions is a critical concern, necessitating the exploration of strategies to enhance plant drought resistance, particularly during the early stages of drought stress. This study focuses on the ectomycorrhizal fungus Cenococcum geophilum, renowned for its extensive genetic diversity and broad host compatibility, making it a crucial ally for host plants facing external stresses. We utilized approximately 5-month-old Pinus massoniana seedlings inoculated with different ecotypic strains of C. geophilum for 7 days of drought stress. The results showed that the inoculation of most strains of C. geophilum enhanced the drought resistance of P. massoniana seedlings under the early stages of drought stress, by influencing the water content, photosynthesis, accumulation of osmotic adjustment substances, and antioxidant enzyme activities in both shoots and roots of seedlings. These responses were further validated through transcriptome analysis. Notably, the level of drought resistance observed in mycorrhizal seedlings was irrespective of the level of drought tolerance of C. geophilum strains. This study contributes essential data for understanding the drought response mechanisms of mycorrhizal P. massoniana seedlings inoculated by distinct C. geophilum ecotypes, and guidance on selecting candidate species of ectomycorrhizal fungi for mycorrhizal afforestation in drought areas.

Mitochondrial alternative oxidase 1a (AOX1a) plays an extremely important role in critical node of seed viability. However, the regulatory mechanism is still poorly understood. The study aims to identify regulatory mechanisms by comparing between OsAOX1a-RNAi and wild type (WT) rice seed during artificial aging treatment. Gain weight and P50 significantly decreased in OsAOX1a-RNAi rice seed, indicating that there might be impaired in seed development and storability. Compared to WT seeds in the 100%, 90%, 80%, and 70% germination, respectively, NADH and succinate-dependent O2 consumption, the activity mitochondrial malate dehydro-genase and ATP contents were decreased in OsAOX1a-RNAi seeds in the 100%, 90%, 80%, and 70% germination, respectively, indicating that mitochondrial status in the OsAOX1a-RNAi seeds after imbibition was weaken than the WT. In addition to, the reduced abundance of complex I N and P module subunits might showed that the capacity of mitochondrial electron transfer chain was significantly inhibited in the OsAOX1a-RNAi seed at critical node of seed viability. Above results might indicated that the ATP production was impaired in OsAOX1a-RNAi seeds during ageing. Therefore, we conclude that the activities of mitochondrial metabolism and alternative pathways were severely inhibited in OsAOX1a-RNAi seeds at critical node of viability, which was leading to accelerate the collapse of seed viability. The precise regulatory mechanism of the alternative pathway at the critical node of viability still needs to be further analyzed.

Circular RNAs (circRNAs) served as covalently closed single-stranded RNAs have been proposed to influence plant development and stress resistance. Grapevine is the most economically valuable fruit crops cultivated worldwide and threaten by various abiotic stresses. Herein, we reported that a circRNA (Vv-circPTCD1) processed from the second exon of a pentatricopeptide repeat family gene PTCD1 was preferentially expressed in leaves and responded to salt and drought but not heat stress in grapevine. Additionally, the second exon sequence of PTCD1 was highly conserved but the biogenesis of Vv-circPTCD1 is species-dependent in plants. It was further found that the overexpressed Vv-circPTCD1 can slightly decreased abundance of the cognate host gene and the neighboring genes were barely affected in grapevine callus. Furthermore, we also successfully overexpressed the Vv-circPTCD1, and found that the Vv-circPTCD1 deteriorated the growth during heat, salt, and drought stresses in Arabidopsis. However, the biological effects on grapevine callus were not always consistent with that of Arabidopsis. Interestingly, we found that the transgenic plants of linear counterpart sequence also conferred the same phenotypes as that of circRNA during the three stress conditions, no matter what species. Those results imply that although the sequences are conserved, the biogenesis and functions of Vv-circPTCD1 are species-dependent. Our results indicate that the plant circRNA function investigation should be conducted in homologous species, which support valuable reference for further plant circRNA studies.