摘要
适度土壤干燥（MSD）是一种很有前景的农业技术，它可以减少水分消耗，促进根鞘形成，提高植物的抗旱能力。内生真菌印度梨形孢（Piriformospora indica）具有很高的生长素产量，可能有利于根鞘的形成。然而，P. indica 与原生土壤微生物群在根鞘形成过程中的综合作用尚不清楚。在此，我们利用高通量测序和水稻突变体研究了籼稻和原生细菌在 MSD 条件下对水稻根鞘形成的作用。在 MSD 条件下，接种 P. indica 后，水稻根鞘的形成显著增加了约 30%。在 MSD 条件下，水稻根部和 P. indica 中的生长素是根鞘形成的原因。其次，在 MSD 条件下，接种 P. indica 后，水稻根鞘和根内的芽孢杆菌属（被称为植物根际促生菌）数量增加。此外，接种 P. indica 还进一步增加了具有高生长素产量的蜡样芽孢杆菌（B. cereus）的数量。同时接种籼稻和蜡样芽孢杆菌后，野生型或叶绿素外流载体 OsPIN2 互补品系水稻的根鞘形成高于 ospin2 突变体。综上所述，我们的研究结果表明，内生真菌 P. indica 与原生土壤细菌 B. cereus 的相互作用通过在MSD条件下调控水稻和微生物的生长素有利于水稻根鞘的形成。这一发现揭示了籼稻内生真菌和原生微生物群在适度土壤干燥条件下对水稻根鞘形成的协同贡献，这对提高农业用水量非常重要。
图 1：接种 P. indica ，在适度土壤干燥（MSD）条件下，增加水稻根鞘的形成。
Fig. 1: Rice rhizosheath formation is increased under moderate soil drying (MSD) with P. indica inoculation compared to MSD alone.
The non-inoculated and P. indica-inoculated rice seedlings (NIP rice) were cultured under well-watered (WW, A, B) and MSD (C, D) conditions. Rice seedlings (NIP rice) were able to form rhizosheath under MSD or MSD with P. indica-inoculation (MSD + P. indica), but not under WW or WW with P. indica-inoculation (WW + P. indica). Bar = 0.5 cm. The total rhizosheath soil dry weight (E) and specific rhizosheath soil dry weight (F) of three rice varieties (NIP, ZH11 and ZH3) under WW, WW + P. indica, MSD and MSD + P. indica. The specific rhizosheath dry weight was calculated as the total rhizosheath soil dry weight per plant (mg) divided by the total root length (cm). N.D. indicated that rhizosheath was not detectable. Data are the means ± SE (n = 8 replicates). Bars with different letters among different treatments are significantly different at p < 0.05 (ANOVA, Duncan’s multiple range test). G, H Fluorescence microscopy of rice seedling (NIP rice) roots showing the presence of intracellular P. indica chlamydospores (spores are in green) in cortical cells using confocal microscopy with a superficial view. The image is an X- and Y-stack reconstruction. Rice roots without GFP-tagged P. indica (P. indica–GFP) inoculation were used as a control. Bar = 150 μm.
图 5：在非灭菌土壤或灭菌土壤中，印度梨形孢和蜡样芽孢杆菌共同接种，通过让生长素外排载体 OsPIN2 基因参与，在适度土壤干燥（MSD）条件下改善了水稻根鞘的形成。
Fig. 5: The rice rhizosheath formation is improved under moderate soil drying (MSD) conditions via co-inoculation with P. indica and Bacillus cereus by involving auxin efflux carrier OsPIN2 gene in non-sterilized soil or sterilized soil.
The specific rhizosheath soil dry weight of rice seedlings (WT, auxin efflux carrier OsPIN2 mutant ospin2 and complementation 1) with non-inoculation (Control), P. indica inoculation (+PI), Bacillus cereus inoculation (+BC), or P. indica and Bacillus cereus co-inoculation (+PI+BC) in non-sterilized soil (A) or sterilized soil (B) under MSD. Data are the means ± SE (n = 8 replicates). Bars with different letters are significantly different at p< 0.05 (ANOVA, Duncan’s multiple range test).
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