Wang Zhihao, Zhang Shiqi, Liang Jingwei, Chen Hui, Jiang Zhijian, Hu Wentao, Tang Ming
State Key Laboratory of Conservation and Utilization of Subtropical Agro-Bioresources, Guangdong Laboratory for Lingnan Modern Agriculture, Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou 510642, China.
Department of Biological Sciences, East Stroudsburg University of Pennsylvania, East Stroudsburg, PA 18301, USA.
Plant Physiol. 2024 Dec 23;197(1). doi: 10.1093/plphys/kiae645.
Arbuscular mycorrhizal fungi (AMF) can transfer inorganic nitrogen (N) from the soil to host plants to cope with drought stress, with arginine synthesis and NH4+ transport being pivotal processes. However, the regulatory mechanism underlying these processes remains unclear. Here, we found that drought stress upregulated expression of genes involved in the N transfer pathway and putrescine and glutathione synthesis in the mycorrhizal structures of Rhizophagus irregularis within alfalfa (Medicago sativa) roots, i.e. carbamoyl phosphate synthase (RiCPSI), arginase (RiCARI), urease (RiURE), ornithine decarboxylase (RiODC), and glutamate-cysteine ligase (RiGCL). Furthermore, we confirmed that RiCPSI is a carbamoyl phosphate synthase. Silencing RiCARI via host-induced gene silencing inhibited arbuscule formation, suppressed putrescine and glutathione synthesis, and altered arginine metabolism within R. irregularis-plant symbiosis, leading to a substantial reduction in the drought tolerance of M. sativa. Conversely, silencing RiCPSI decreased arginine, putrescine, and glutathione synthesis in R. irregularis but did not adversely affect NH4+ transfer from fungi to the host plant and drought tolerance of M. sativa. Interestingly, overexpressing RiCPSI via our host-induced gene overexpressing system enhanced arginine, putrescine, and glutathione synthesis in R. irregularis, reduced arbuscule abundance, and improved drought tolerance of M. sativa. Our findings demonstrate that under drought stress, the nitrogen transfer from AMF to the host plant was improved. This is accompanied by increased arginine, putrescine, and glutathione synthesis within R. irregularis, driven by the upregulation of RiCPSI and RiCARI expression in mycorrhizal structures within the roots. These molecular adjustments collectively contribute to enhanced drought tolerance in R. irregularis-plant symbiosis.
丛枝菌根真菌（AMF）可将土壤中的无机氮（N）转移至宿主植物，以应对干旱胁迫，其中精氨酸合成和NH4+转运是关键过程。然而，这些过程背后的调控机制仍不清楚。在此，我们发现干旱胁迫上调了紫花苜蓿（Medicago sativa）根内不规则球囊霉（Rhizophagus irregularis）菌根结构中参与氮转移途径以及腐胺和谷胱甘肽合成的基因表达，即氨甲酰磷酸合成酶（RiCPSI）、精氨酸酶（RiCARI）、脲酶（RiURE）、鸟氨酸脱羧酶（RiODC）和谷氨酸-半胱氨酸连接酶（RiGCL）。此外，我们证实RiCPSI是一种氨甲酰磷酸合成酶。通过宿主诱导基因沉默使RiCARI沉默会抑制丛枝形成，抑制腐胺和谷胱甘肽合成，并改变不规则球囊霉与植物共生体中的精氨酸代谢，导致紫花苜蓿耐旱性大幅降低。相反，使RiCPSI沉默会降低不规则球囊霉中精氨酸、腐胺和谷胱甘肽的合成，但不会对真菌向宿主植物的NH4+转移以及紫花苜蓿的耐旱性产生不利影响。有趣的是，通过我们的宿主诱导基因过表达系统过表达RiCPSI可增强不规则球囊霉中精氨酸、腐胺和谷胱甘肽的合成，减少丛枝丰度，并提高紫花苜蓿的耐旱性。我们的研究结果表明，在干旱胁迫下，AMF向宿主植物的氮转移得到改善。这伴随着不规则球囊霉中精氨酸、腐胺和谷胱甘肽合成的增加，这是由根内菌根结构中RiCPSI和RiCARI表达上调驱动的。这些分子调节共同有助于增强不规则球囊霉与植物共生体的耐旱性。
