Navarro R E, Aguirre J
Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510 México, D.F.
J Bacteriol. 1998 Nov;180(21):5733-8. doi: 10.1128/JB.180.21.5733-5738.1998.
Two differentially regulated catalase genes have been identified in the fungus Aspergillus nidulans. The catA gene belongs to a class whose transcripts are specifically induced during asexual sporulation (conidiation) and encodes a catalase accumulated in conidia. Using a developmental mutant affected in the brlA gene, which is unable to form conidia but capable of producing sexual spores (ascospores), we demonstrated that the catA mRNA accumulated during induction of conidiation but did not produce CatA protein. In contrast, high levels of catalase A activity were detected in the ascospores produced by this mutant, indicating that the catA gene is posttranscriptionally regulated. The same type of regulation was observed for a catA::lacZ translational gene fusion, suggesting that the catA message 5' untranslated region could be involved in translational control during development. In a wild-type strain, beta-galactosidase activity driven from the catA::lacZ gene fusion was low in hyphae and increased 50-fold during conidiation and 620-fold in isolated conidia. Consistent with this finding spatial expression of the reporter gene was restricted to metulae, phialides, and conidia. Conidium-associated expression was maintained in a stuA mutant, in which the conidiophore cell pattern is severely deranged. catA mRNA accumulation was also observed when vegetative mycelia was subject to oxidative, osmotic, and nitrogen or carbon starvation stress. Nevertheless, catalase A activity was restricted to the conidia produced under nutrient starvation. Our results provide support for a model in which translation of the catA message, accumulated during conidiation or in response to different types of stress, is linked to the morphogenetic processes involved in asexual and sexual spore formation. Our findings also indicate that brlA-independent mechanisms regulate the expression of genes encoding spore-specific products.
在真菌构巢曲霉中已鉴定出两个差异调节的过氧化氢酶基因。catA基因属于一类，其转录本在无性孢子形成（产孢）过程中被特异性诱导，并编码一种在分生孢子中积累的过氧化氢酶。利用一个受brlA基因影响的发育突变体，该突变体无法形成分生孢子但能够产生有性孢子（子囊孢子），我们证明catA mRNA在分生孢子形成诱导过程中积累，但不产生CatA蛋白。相反，在该突变体产生的子囊孢子中检测到高水平的过氧化氢酶A活性，这表明catA基因是转录后调控的。对于catA::lacZ翻译基因融合也观察到相同类型的调控，这表明catA信息的5'非翻译区可能参与发育过程中的翻译控制。在野生型菌株中，由catA::lacZ基因融合驱动的β-半乳糖苷酶活性在菌丝中较低，在分生孢子形成过程中增加50倍，在分离的分生孢子中增加620倍。与这一发现一致，报告基因的空间表达仅限于梗基、小梗和分生孢子。分生孢子相关的表达在stuA突变体中得以维持，在该突变体中分生孢子梗细胞模式严重紊乱。当营养菌丝体受到氧化、渗透、氮或碳饥饿胁迫时，也观察到catA mRNA的积累。然而，过氧化氢酶A活性仅限于在营养饥饿条件下产生的分生孢子。我们的结果支持了一个模型，即在分生孢子形成过程中或对不同类型胁迫作出反应时积累的catA信息的翻译与参与无性和有性孢子形成的形态发生过程相关联。我们的发现还表明，不依赖brlA的机制调节编码孢子特异性产物的基因的表达。
