AgResearch Limited, Grasslands Research Centre, Palmerston North, New Zealand.
Mol Plant Pathol. 2023 Nov;24(11):1430-1442. doi: 10.1111/mpp.13379. Epub 2023 Jul 21.
Epichloë festucae uses a siderophore-mediated system to acquire iron, which is important to maintain endophyte-grass symbioses. Here we investigate the roles of the alternative iron acquisition system, reductive iron assimilation (RIA), via disruption of the fetC gene, which encodes a multicopper ferroxidase, either alone (i.e., ΔfetC) or in combination with disruption of the gene sidA, which encodes a siderophore biosynthesis enzyme (i.e., ΔfetC/ΔsidA). The phenotypic characteristics of these mutants were compared to ΔsidA and wild-type (WT) strains during growth under axenic culture conditions (in culture) and in symbiosis with the host grass, perennial ryegrass (in planta). Under iron deficiency, the colony growth rate of ΔfetC was slightly slower than that of WT, while the growth of ΔsidA and ΔfetC/ΔsidA mutants was severely suppressed. Siderophore analyses indicated that ΔfetC mutants hyperaccumulate ferriepichloënin A (FEA) at low iron concentrations and ferricrocin and FEA at higher iron concentrations. When compared to WT, all mutant strains displayed hyperbranching hyphal structures and a reduced ratio of Epichloë DNA to total DNA in planta. Furthermore, host colonization and vertical transmission through infection of the host seed were significantly reduced in the ΔfetC/ΔsidA mutants, confirming that high-affinity iron uptake is a critical process for Epichloë transmission. Thus, RIA and siderophore iron uptake are complementary systems required for the maintenance of iron metabolism, fungal growth, and symbiosis between E. festucae and perennial ryegrass.
雀麦内生真菌利用铁载体介导系统获取铁，这对维持内生真菌-草共生体至关重要。在这里，我们通过破坏编码多铜氧化酶的 fetC 基因（即 ΔfetC），或与破坏编码铁载体生物合成酶的基因 sidA 的破坏（即 ΔfetC/ΔsidA），来研究还原性铁同化（RIA）等替代铁获取系统的作用。这些突变体的表型特征与缺失 sidA 基因（即 ΔsidA）和野生型（WT）菌株在无菌培养条件下生长（在培养中）和与宿主黑麦草共生（在植物中）的特征进行了比较。在缺铁条件下，ΔfetC 的菌落生长速度比 WT 略慢，而 ΔsidA 和 ΔfetC/ΔsidA 突变体的生长则受到严重抑制。铁载体分析表明，ΔfetC 突变体在低铁浓度下大量积累铁载体雀麦镰孢素 A（FEA），而在高铁浓度下则积累 ferricrocin 和 FEA。与 WT 相比，所有突变株在植物体内都表现出菌丝过度分枝结构和 Epichloë DNA 与总 DNA 的比例降低。此外，ΔfetC/ΔsidA 突变体对宿主的定殖和通过感染宿主种子的垂直传播显著减少，这证实了高亲和力铁摄取是雀麦内生真菌传播的关键过程。因此，RIA 和铁载体铁摄取是维持铁代谢、真菌生长和雀麦内生真菌与多年生黑麦草共生关系所必需的互补系统。
