Rio Maria Carolina S do, de Oliveira Bruno V, de Tomazella Daniela P T, Silva José A Fracassi da, Pereira Gonçalo A G
Departamento de Genética e Evolução, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, 13083-970, São Paulo, Brazil.
Curr Microbiol. 2008 Apr;56(4):363-70. doi: 10.1007/s00284-007-9091-7. Epub 2008 Jan 3.
Oxalic acid has been shown as a virulence factor for some phytopathogenic fungi, removing calcium from pectin and favoring plant cell wall degradation. Recently, it was published that calcium oxalate accumulates in infected cacao tissues during the progression of Witches' Broom disease (WBD). In the present work we report that the hemibiotrophic basidiomycete Moniliophthora perniciosa, the causal agent of WBD, produces calcium oxalate crystals. These crystals were initially observed by polarized light microscopy of hyphae growing on a glass slide, apparently being secreted from the cells. The analysis was refined by Scanning electron microscopy and the compositon of the crystals was confirmed by energy-dispersive x-ray spectrometry. The production of oxalate by M. perniciosa was reinforced by the identification of a putative gene coding for oxaloacetate acetylhydrolase, which catalyzes the hydrolysis of oxaloacetate to oxalate and acetate. This gene was shown to be expressed in the biotrophic-like mycelia, which in planta occupy the intercellular middle-lamella space, a region filled with pectin. Taken together, our results suggest that oxalate production by M. perniciosa may play a role in the WBD pathogenesis mechanism.
草酸已被证明是一些植物病原真菌的致病因子，它能从果胶中去除钙，有利于植物细胞壁的降解。最近有报道称，在女巫扫帚病（WBD）的发展过程中，草酸钙在受感染的可可组织中积累。在本研究中，我们报告了WBD的病原菌——半活体营养担子菌可可球二孢菌会产生草酸钙晶体。这些晶体最初是通过偏光显微镜观察在载玻片上生长的菌丝而发现的，显然是从细胞中分泌出来的。通过扫描电子显微镜对分析进行了细化，并通过能量色散X射线光谱法确认了晶体的成分。通过鉴定一个编码草酰乙酸乙酰水解酶的推定基因，进一步证实了可可球二孢菌能产生草酸盐，该酶催化草酰乙酸水解为草酸盐和乙酸盐。该基因在类似活体营养的菌丝体中表达，这些菌丝体在植物体内占据充满果胶的细胞间中层空间。综上所述，我们的结果表明，可可球二孢菌产生草酸盐可能在WBD发病机制中起作用。
