The effectiveness of microbial inoculants in agriculture is often limited by their unstable colonization in dynamic soil environments. We investigated the impact of application timing and continuity of a four-member synthetic microbial community (SynCom) on pepper (Capsicum annuum L.) productivity and rhizosphere microbiome dynamics under greenhouse conditions. Four treatments were included: no inoculation (control), single inoculation at the seedling stage (T1; 5 days post-emergence), single inoculation at the potting stage (T2; 14 days post-transplant), and sustained inoculation at both stages (T3). T3 significantly enhanced plant dry weight (113.4%), root activity (267.8%), fruit sugar (43.9%), and yield (29.0%) relative to the control; and profoundly reshaped the rhizosphere microbiome, enriching functional pathways for nutrient cycling (e.g., phosphorus, nitrogen, and potassium metabolism) and phytohormone synthesis (e.g., indoleacetic acid pathway). Co-occurrence network analysis indicated a significant alteration in microbial interaction patterns, revealing a new community architecture with key taxa such as Neocosmospora, Dyella and the Rhizobium group emerging as central hubs in the T3 network. Our findings underscore that application continuity is a critical factor for optimizing bio-inoculant efficacy, providing a strategy to enhance crop productivity through microbiome engineering in sustainable agriculture.

Plants frequently encounter relatively low and fluctuating potassium (K⁺) concentrations in soil, with roots serving as primary responders to this stress. Histone modifications, such as de-/acetylation, can function as epigenetic markers of stress-inducible genes. However, the signaling network between histone modifications and low-K⁺ (LK) response pathways remains unclear. This study investigated the regulatory role of Histone Deacetylase Complex 1 (HDC1) in primary root growth of Arabidopsis thaliana under K⁺ deficiency stress. Using a hdc1-2 mutant line, we observed that HDC1 positively regulated root growth under LK conditions. Compared to wild-type (WT) plants, the hdc1-2 mutant exhibited significantly inhibited primary root growth under LK conditions, whereas HDC1-overexpression lines displayed opposite phenotypes. No significant differences were observed under HK conditions. Further analysis revealed that the inhibition of hdc1-2 on root growth was due to reduced apical meristem cell proliferation rather than cell elongation. Notably, the root growth of hdc1-2 showed reduced sensitivity compared to WT after auxin treatment under LK conditions. HDC1 may regulate root growth by affecting auxin polar transport and subsequent auxin signaling, as evidenced by the altered expression of auxin transport genes. Moreover, the organ-specific RT-qPCR analyses unraveled that HDC1 negatively regulates the expression of CBL-CIPK-K⁺ channel-related genes such as CBL1, CBL2, CBL3, AKT1, and TPK1, thereby establishing a molecular link between histone deacetylation, auxin signaling, and CBLs-CIPKs pathway in response to K⁺ deficiency.

Plants frequently encounter relatively low and fluctuating potassium (K+) concentrations in soil, with roots serving as the primary responders to this stress. Histone modifications, such as de-/acetylation, can function as epigenetic marks on stress-inducible genes. However, the signaling network between histone modifications and the low K+ (LK) response pathways remains unclear. This study delves into the regulatory role of Histone Deacetylase Complex 1 (HDC1) in primary root growth of Arabidopsis thaliana under K+ deficiency stress. Using a hdc1-2 mutant line, we observed that HDC1 positively regulates root growth under LK conditions. Compared to wild-type (WT) plants, the hdc1-2 mutant exhibited significantly inhibited primary root growth under LK conditions, whereas HDC1-overexpression lines displayed opposite phenotypes. No significant difference was observed under HK conditions. Further analysis revealed that the inhibition of hdc1-2 on root growth was due to reduced meristem cell proliferation rather than cell elongation. Notably, the root growth of hdc1-2 shows reduced sensitivity compared to WT after auxin treatment under LK conditions. HDC1 may regulate root growth by affecting auxin polar transport and subsequently auxin sensation, as evidenced by altered expression of auxin transport genes. Moreover, our study reveals a brake function of HDC1 in the regulation of CBL-CIPK-K+ channel related genes, thereby establishing a molecular link between histone deacetylation, auxin signaling, and CBL-CIPK pathway in response to K+ deficiency.