The tangerine pathotype of Alternaria alternata affects many citrus cultivars, resulting in yield losses. The capability to produce the host-selective toxin and cell-wall-degrading enzymes and to mitigate toxic reactive oxygen species is crucial for A. alternata pathogenesis to citrus. Little is known about nutrient availability within citrus tissues to the fungal pathogen. In the present study, we assess the infectivity of a biotin deficiency mutant (ΔbioB) and a complementation strain (CP36) on citrus leaves to determine how biotin impacts A. alternata pathogenesis. Growth and sporulation of ΔbioB are highly dependent on biotin. ΔbioB retains its ability to acquire and transport biotin from the surrounding environment. Growth deficiency of ΔbioB can also be partially restored by the presence of oleic acid or Tween 20, suggesting the requirement of biotin in lipid metabolism. Experimental evidence indicates that de novo biotin biosynthesis is regulated by the NADPH oxidase, implicating in the production of H₂O₂, and is affected by the function of peroxisomes. Three genes involved in the biosynthesis of biotin are clustered and co-regulated by biotin indicating a transcriptional feedback loop activation. Infectivity assays using fungal mycelium reveal that ΔbioB cultured on medium without biotin fails to infect citrus leaves; co-inoculation with biotin fully restores infectivity. The CP36 strain re-expressing a functional copy of bioB displays wild-type growth, sporulation and virulence. Taken together, we conclude that the attainability or accessibility of biotin is extremely restricted in citrus cells. A. alternata must be able to synthesize biotin in order to utilize nutrients for growth, colonization and development within the host.

链格孢菌的橘子病态影响许多柑橘品种，导致产量损失。产生宿主选择性毒素和降解细胞壁的酶以及减轻有毒的活性氧的能力对于柑橘交链孢霉的发病机理至关重要。人们对柑橘组织内真菌病原体的养分利用率知之甚少。在本研究中，我们评估生物素缺乏突变体的感染性（Δ bioB）和柑桔叶一个互补株（CP36），以确定如何影响生物素A.孢发病机理。Δ的生长和产孢bioB高度依赖于生物素。Δ bioB保留了从周围环境中获取和运输生物素的能力。ΔbioB的生长缺陷还可以通过油酸或Tween 20的存在而部分恢复，这表明脂质代谢中需要生物素。实验证据表明，从头生物素的生物合成受到NADPH氧化酶的调节，与H ₂ O ₂的产生有关，并且受过氧化物酶体功能的影响。涉及生物素生物合成的三个基因被生物素聚集并共同调节，表明转录反馈环被激活。使用真菌菌丝体的感染性测定表明ΔbioB在没有生物素的培养基上培养无法感染柑橘叶片；与生物素共同接种可完全恢复感染力。重新表达bioB功能拷贝的CP36菌株显示出野生型生长，孢子形成和毒力。两者合计，我们得出结论，在柑橘类细胞中，生物素的可获得性或可及性受到极大限制。交替链霉菌必须能够合成生物素，以便利用营养物质在宿主体内生长，定植和发展。