The BASIC PENTACYSTEIENE transcription factors interact with type-A Arabidopsis response regulators and regulate a sub-s

The type-A Arabidopsis Response Regulators (ARRs) are cytokinin primary response genes that negatively regulate the cytokinin signaling pathway. Here we identify members of the BASIC PENTACYSTIENE (BPC) transcription factor gene family as interacting with a subset of type-A ARR proteins in Arabidopsis thaliana and characterize their role in cytokinin signaling. Members of the BPC family interacted with type-A ARRs based on yeast two-hybrid and co-immunoprecipitation assays. bpc multiple mutants show reduced sensitivity to cytokinin in root elongation assays. The BPCs are necessary for induction of a subset of genes in response to exogenous cytokinin. Furthermore, a significant number of genes whose expression is altered in bpc mutant roots are also mis-expressed in cytokinin response factor (crf1,3,5,6) mutant and type-A arr3,4,5,6,7,8,9,15 mutant roots, suggesting interplay among these elements. BPC6 binds to the promoters of cytokinin-regulated genes and a significant number of BPC6 regulated-genes are also targets of the type-B ARR transcription factors, which are activated in response to cytokinin. These results suggest that the BPCs are part of a complex network of transcription factors that are involved in the response to cytokinin and the interaction of the BPCs with the type-A ARRs likely modifies this regulation.

A型拟南芥反应调节因子（type-A Arabidopsis Response Regulators, ARRs）是一类负调控细胞分裂素信号通路的细胞分裂素初级响应基因。本研究鉴定到碱性五半胱氨酸（BASIC PENTACYSTIENE, BPC）转录因子基因家族的成员可与拟南芥中的部分A型ARRs蛋白相互作用，并解析了其在细胞分裂素信号通路中的功能。通过酵母双杂交与免疫共沉淀实验证实，BPC家族成员可与A型ARRs发生互作。bpc多突变体在根伸长实验中对细胞分裂素的敏感性显著降低。BPC家族成员对于外源细胞分裂素诱导的部分基因的表达是必需的。此外，在bpc突变体根中表达发生改变的大量基因，同样在细胞分裂素响应因子（cytokinin response factor, CRF1、3、5、6）突变体以及A型ARR3、4、5、6、7、8、9、15突变体的根中存在表达异常，提示这些调控元件之间存在相互调控关系。BPC6可结合受细胞分裂素调控的基因的启动子区域，且受BPC6调控的大量基因同时也是B型ARRs转录因子（type-B ARR transcription factors）的靶标，而B型ARRs可响应细胞分裂素被激活。上述结果表明，BPC家族成员参与构成了调控细胞分裂素响应的复杂转录调控网络，且BPC与A型ARRs的相互作用可能会修饰这一调控过程。