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In arbuscular mycorrhizal (AM) symbiosis, appropriate regulation of the formation, maintenance, and degeneration of the arbuscule are essential for plants and fungi. In this study, we identified a Cysteine-2/Histidine-2 zinc finger protein (C2H2-ZFP)-encoding gene in Lotus japonicus named Regulator of Symbiosome Differentiation-Like (LjRSDL) that is required for arbuscule degeneration. Evolutionary analysis showed that homologs of LjRSDL exist in mycorrhizal flowering plants. We obtained ProLjRSDL::GUS transgenic hairy roots and showed that LjRSDL was strongly upregulated upon AM colonization, particularly at 18 days post AM fungi inoculation and specifically expressed in arbuscular-containing cells. The mycorrhization rate increased in the ljrsdl mutant but decreased in LjRSDL overexpressed L. japonicus. Interestingly, we observed higher proportions of large arbuscule in the ljrsdl mutant but lower proportions of larger arbuscule in LjRSDL overexpressing plants. Transcriptome analyses indicated that genes involved in arbuscule degeneration were significantly changed upon the dysregulation of LjRSDL and that LjRSDL-dependent regulation in AM symbiosis is mainly via the hormone signal transduction pathway. LjRSDL, therefore, represents a C2H2-ZFP that negatively regulates AM symbiosis. Our study provides insight into understanding plant-AM fungal communication and AM symbiosis development.

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The SWEETs (sugars will eventually be exported transporter) family comprises a class of recently identified sugar transporters that play diverse roles in regulating plant development. Beyond those fundamental functions, emerging evidence suggests that SWEETs may also be involved in plant stress responses, such as salt tolerance. However, the specific role of maize SWEETs in regulating salt tolerance remains unexplored. In this study, we demonstrate that two maize SWEET family members, ZmSWEET15a and ZmSWEET15b, are typical sugar transporters with seven transmembrane helices localized in the cell membrane. The heterologous expression of ZmSWEET15a and ZmSWEET15b in the yeast mutant strain confirms their role as sucrose transporters. Overexpression of ZmSWEET15a and ZmSWEET15b in Arabidopsis resulted in improved NaCl resistance and significant increase in seed germination rate compared to the wild type. Furthermore, by generating maize knockout mutants, we observe that the absence of ZmSWEET15a and ZmSWEET15b affects both plant growth and grain development. The salt treatment results indicate that the knockout mutants of these two genes are more sensitive to salt stress. Comparative analyses revealed that wild-type maize plants outperformed the knockout mutants in terms of growth parameters and physiological indices. Our findings unravel a novel function of ZmSWEET15a and ZmSWEET15b in the salt stress response, offering a theoretical foundation for enhancing maize salt resistance.

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Soil microbial communities are essential to biogeochemical cycles. However, the responses of microorganisms in volcanic soil with high heavy metal levels remain poorly understood. Here, two areas with high levels of cadmium (Cd) from the same volcano were investigated to determine their archaeal composition and assembly. In this study, the Cd concentrations (0.32-0.38 mg/ kg) in the volcanic soils exceeded the standard risk screening values (GB15618-2018) and correlated with archaeal communities strongly (P < 0.05). Moreover, the area with elevated levels of Cd (periphery) exhibited a greater diversity of archaeal species, albeit with reduced archaeal activity, compared to the area with lower levels of Cd (center). Besides, stochastic processes mainly governed the archaeal communities. Furthermore, the co-occurrence network was simplest in the periphery. The proportion of positive links between taxa increased positively with Cd concentration. Moreover, four keystone taxa (all from the family Nitrososphaeraceae) were identified from the archaeal networks. In its entirety, this study has expanded our comprehension of the variations of soil archaeal communities in volcanic areas with elevated cadmium levels and serves as a point of reference for the agricultural development of volcanic soils in China.

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Drought stress often affects crop growth and even causes crop death, while aquaporins can maintain osmotic balance by transporting water across membranes, so it is important to study how to improve drought tolerance of crops by using aquaporins. In this work, we characterize a set of subfamily members named NIPs belonging to the family of aquaporins in Lotus japonicus, grouping 14 family members based on the sequence similarity in the aromatic/arginine (Ar/R) region. Among these members, LjNIP1;5 is one of the genes with the highest expression in roots which is induced by the AM fungus. In Lotus japonicus, LjNIP1;5 is highly expressed in symbiotic roots, and its promoter can be induced by drought stress and AM fungus. Root colonization analysis reveals that ljnip1:5 mutant exhibits lower mycorrhizal colonization than the wild type, with increasing the proportion of large arbuscule, and fewer arbuscule produced by symbiosis under drought stress. In the LjNIP1;5OE plant, we detected a strong antioxidant capacity compared to the control, and LjNIP1;5OE showed higher stem length under drought stress. Taken together, the current results facilitate our comprehensive understanding of the plant adaptive to drought stress with the coordination of the specific fungi.

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The symbiosis with arbuscular mycorrhizal (AM) fungi improves plants' nutrient uptake. During this process, transcription factors have been highlighted to play crucial roles. Members of the GRAS transcription factor gene family have been reported involved in AM symbiosis, but little is known about SCARECROW-LIKE3 (SCL3) genes belonging to this family in Lotus japonicus. In this study, 67 LjGRAS genes were identified from the L. japonicus genome, seven of which were clustered in the SCL3 group. Three of the seven LjGRAS genes expression levels were upregulated by AM fungal inoculation, and our biochemical results showed that the expression of LjGRAS36 was specifically induced by AM colonization. Functional loss of LjGRAS36 in mutant ljgras36 plants exhibited a significantly reduced mycorrhizal colonization rate and arbuscular size. Transcriptome analysis showed a deficiency of LjGRAS36 led to the dysregulation of the gibberellic acid signal pathway associated with AM symbiosis. Together, this study provides important insights for understanding the important potential function of SCL3 genes in regulating AM symbiotic development. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-022-01161-z.