Phosphorus is one of the most important macronutrients required for plant growth and development. The importance of phosphorylation modification in regulating phosphate (Pi) homeostasis in plants is emerging. We performed phosphoproteomic profiling to characterize proteins whose degree of phosphorylation is altered in response to Pi starvation in rice root. A subset of 554 proteins, including 546 down-phosphorylated and eight up-phosphorylated proteins, exhibited differential phosphorylation in response to Pi starvation. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis with the differentially phosphorylated proteins indicated that RNA processing, transport, splicing and translation and carbon metabolism played critical roles in response to Pi starvation in rice. Levels of phosphorylation of four mitogen-activated protein kinases (MAPKs), including OsMAPK6, five calcium-dependent protein kinases (CDPKs) and OsCK2β3 decreased in response to Pi starvation. The decreased phosphorylation level of OsMAPK6 was confirmed by Western blotting. Mutation of OsMAPK6 led to Pi accumulation under Pi-sufficient conditions. Motif analysis indicated that the putative MAPK, casein kinase 2 (CK2) and CDPK substrates represented about 54.4%, 21.5% and 4.7%, respectively, of the proteins exhibiting differential phosphorylation. Based on the motif analysis, 191, 151 and 46 candidate substrates for MAPK, CK2 and CDPK were identified. These results indicate that modification of phosphorylation profiles provides complementary information on Pi-starvation-induced processes, with CK2, MAPK and CDPK protein kinase families playing key roles in these processes in rice.

中文翻译：

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磷酸化蛋白质组分析揭示了水稻对磷饥饿的反应中CK2，MAPKs和CDPKs的重要性。

磷是植物生长发育所需的最重要的常量营养素之一。磷酸化修饰在调节植物磷酸盐（Pi）稳态中的重要性正在兴起。我们进行了磷酸化蛋白质组分析，以表征其蛋白质的磷酸化程度响应于水稻根中Pi饥饿而改变的蛋白质。554种蛋白质的子集（包括546种下磷酸化和8种上磷酸化的蛋白质）在响应Pi饥饿时表现出不同的磷酸化。《京都市基因与基因组百科全书》（KEGG）对磷酸化差异蛋白的分析表明，RNA的加工，转运，剪接和翻译以及碳代谢在水稻对Pi饥饿的反应中起着至关重要的作用。响应Pi饥饿，包括OsMAPK6，五个钙依赖性蛋白激酶（CDPKs）和OsCK2β3在内的四种促分裂原活化蛋白激酶（MAPK）的磷酸化水平降低。通过蛋白质印迹证实OsMAPK6的磷酸化水平降低。OsMAPK6的突变导致Pi在充足的条件下积累。基序分析表明，推定的MAPK，酪蛋白激酶2（CK2）和CDPK底物分别占显示差异磷酸化的蛋白质的约54.4％，21.5％和4.7％。基于基序分析，鉴定出191、151和46种MAPK，CK2和CDPK的候选底物。这些结果表明，磷酸化图谱的修饰可提供有关CK2与Pi饥饿诱导的过程有关的补充信息，