Australian Research Council Centre of Excellence in Plant Energy Biology, Research School of Biology, Australian National University Canberra, Acton, Australian Capital Territory 0200, Australia.
Plant Cell. 2011 Nov;23(11):3992-4012. doi: 10.1105/tpc.111.091033. Epub 2011 Nov 29.
Compartmentation of the eukaryotic cell requires a complex set of subcellular messages, including multiple retrograde signals from the chloroplast and mitochondria to the nucleus, to regulate gene expression. Here, we propose that one such signal is a phosphonucleotide (3'-phosphoadenosine 5'-phosphate [PAP]), which accumulates in Arabidopsis thaliana in response to drought and high light (HL) stress and that the enzyme SAL1 regulates its levels by dephosphorylating PAP to AMP. SAL1 accumulates in chloroplasts and mitochondria but not in the cytosol. sal1 mutants accumulate 20-fold more PAP without a marked change in inositol phosphate levels, demonstrating that PAP is a primary in vivo substrate. Significantly, transgenic targeting of SAL1 to either the nucleus or chloroplast of sal1 mutants lowers the total PAP levels and expression of the HL-inducible ASCORBATE PEROXIDASE2 gene. This indicates that PAP must be able to move between cellular compartments. The mode of action for PAP could be inhibition of 5' to 3' exoribonucleases (XRNs), as SAL1 and the nuclear XRNs modulate the expression of a similar subset of HL and drought-inducible genes, sal1 mutants accumulate XRN substrates, and PAP can inhibit yeast (Saccharomyces cerevisiae) XRNs. We propose a SAL1-PAP retrograde pathway that can alter nuclear gene expression during HL and drought stress.
真核细胞的区隔化需要一套复杂的细胞内信息，包括来自叶绿体和线粒体的多个逆行信号到细胞核，以调节基因表达。在这里，我们提出，这样的信号之一是一个磷酸核苷酸（3'-磷酸腺苷 5'-磷酸[PAP]），它在拟南芥中积累响应干旱和高光（HL）胁迫，并且酶 SAL1 通过去磷酸化 PAP 调节其水平到 AMP。SAL1 在叶绿体和线粒体中积累，但不在细胞质中。sal1 突变体积累 20 倍以上的 PAP，而肌醇磷酸盐水平没有明显变化，表明 PAP 是一种主要的体内底物。重要的是，将 SAL1 转基因靶向 sal1 突变体的核或叶绿体可降低总 PAP 水平和 HL 诱导的 ASCORBATE PEROXIDASE2 基因的表达。这表明 PAP 必须能够在细胞区室之间移动。PAP 的作用模式可能是抑制 5'到 3'外切核酸酶（XRNs），因为 SAL1 和核 XRNs 调节类似的 HL 和干旱诱导基因表达的子集，sal1 突变体积累 XRN 底物，并且 PAP 可以抑制酵母（酿酒酵母）XRNs。我们提出了一个 SAL1-PAP 逆行途径，可以在 HL 和干旱胁迫期间改变核基因表达。
