Hall A A, Bindslev L, Rouster J, Rasmussen S W, Oliver R P, Gurr S J
Department of Plant Sciences, University of Oxford, U.K.
Mol Plant Microbe Interact. 1999 Nov;12(11):960-8. doi: 10.1094/MPMI.1999.12.11.960.
Erysiphe graminis f. sp. hordei, the causal agent of barley powdery mildew, is an obligate biotroph. On arrival on the host, a primary germ tube (PGT) emerges from the conidium. An appressorial germ tube (AGT) then appears, forms an appressorium, and effects host penetration. Such developmental precision may be due to multiple, plant-derived signals and to endogenous tactile and chemical signals. The transduction mechanism remains obscure. The isolation of an expressed sequence tag (EST) homologue of the catalytic subunit of cyclic AMP (cAMP)-dependent protein kinase A (PKA) enabled the corresponding gene to be characterized and the transcript to be identified in conidia and in PGT and AGT stage spores. cAMP-dependent PKA activity was detected in ungerminated conidia. These data suggest that PKA and cAMP are involved in conidial development. To substantiate this we exploited the responses of developing conidia to various surfaces, including exposure to the host leaf (fully inductive to AGT formation), cellulose membrane (semi-inductive), and glass (non-inductive). Assessment of fungal development, following application of exogenous cAMP or cAMP analogues, revealed that, at different concentrations and on different surfaces, cAMP either promoted or inhibited conidial differentiation. Various PKA inhibitors were tested for their effect on PKA activity and conidial development. A negative correlation was established between PKA inhibition in vitro and fungal development in vivo. Taken collectively, these data suggest that PKA and cAMP play a role in conidial differentiation in this obligate, plant-pathogenic fungus.
大麦白粉病的病原菌禾本科布氏白粉菌是一种专性活体营养型真菌。分生孢子落到寄主上后，会伸出一根初生芽管（PGT）。接着出现附着胞芽管（AGT），形成附着胞，并实现对寄主的穿透。这种发育的精确性可能归因于多种植物来源的信号以及内源性触觉和化学信号。其转导机制仍不清楚。一个与环磷酸腺苷（cAMP）依赖性蛋白激酶A（PKA）催化亚基的表达序列标签（EST）同源物的分离，使得相应基因得以鉴定，并在分生孢子以及PGT和AGT阶段的孢子中鉴定出转录本。在未萌发的分生孢子中检测到了cAMP依赖性PKA活性。这些数据表明PKA和cAMP参与了分生孢子的发育。为了证实这一点，我们利用了发育中的分生孢子对各种表面的反应，包括暴露于寄主叶片（对AGT形成完全诱导）、纤维素膜（半诱导）和玻璃（非诱导）。在施加外源cAMP或cAMP类似物后对真菌发育进行评估，结果显示，在不同浓度和不同表面上，cAMP要么促进要么抑制分生孢子的分化。测试了各种PKA抑制剂对PKA活性和分生孢子发育的影响。在体外PKA抑制与体内真菌发育之间建立了负相关。总体而言，这些数据表明PKA和cAMP在这种专性植物病原真菌的分生孢子分化中发挥作用。
