Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, VIC, 3052, Australia.
AgriBio, La Trobe University, Bundoora, VIC, 3083, Australia.
Plant J. 2017 Aug;91(4):590-600. doi: 10.1111/tpj.13589. Epub 2017 Jun 12.
The brassinosteroid receptor brassinosteroid insensitive 1 (BRI1) is a member of the leucine-rich repeat receptor-like kinase family. The intracellular kinase domain of BRI1 is an active kinase and also encapsulates a guanylate cyclase catalytic centre. Using liquid chromatography tandem mass spectrometry, we confirmed that the recombinant cytoplasmic domain of BRI1 generates pmol amounts of cGMP per μg protein with a preference for magnesium over manganese as a co-factor. Importantly, a functional BRI1 kinase is essential for optimal cGMP generation. Therefore, the guanylate cyclase activity of BRI1 is modulated by the kinase while cGMP, the product of the guanylate cyclase, in turn inhibits BRI1 kinase activity. Furthermore, we show using Arabidopsis root cell cultures that cGMP rapidly potentiates phosphorylation of the downstream substrate brassinosteroid signaling kinase 1 (BSK1). Taken together, our results suggest that cGMP acts as a modulator that enhances downstream signaling while dampening signal generation from the receptor.
油菜素内酯受体油菜素内酯不敏感 1（BRI1）是富含亮氨酸重复受体样激酶家族的成员。BRI1 的细胞内激酶结构域是一种活性激酶，同时还包含鸟苷酸环化酶催化中心。使用液相色谱串联质谱法，我们证实重组的 BRI1 细胞质结构域每微克蛋白可产生 pmol 数量的 cGMP，并且优先选择镁而不是锰作为辅助因子。重要的是，BRI1 激酶的功能对于最佳的 cGMP 生成是必需的。因此，BRI1 的鸟苷酸环化酶活性受到激酶的调节，而鸟苷酸环化酶的产物 cGMP 反过来又抑制 BRI1 激酶活性。此外，我们通过拟南芥根细胞培养表明 cGMP 可快速增强下游底物油菜素内酯信号激酶 1（BSK1）的磷酸化。总之，我们的结果表明 cGMP 作为一种调节剂，增强了下游信号，同时抑制了受体的信号生成。
