Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo, 184-8588 Japan.
CSIRO Agriculture and Food, Canberra, ACT 2601, Australia.
Plant Cell Physiol. 2019 Dec 1;60(12):2758-2768. doi: 10.1093/pcp/pcz163.
Abscisic acid (ABA) is a phytohormone and a major determinant of seed dormancy in plants. Seed dormancy is gradually lost during dry storage, a process known as 'after-ripening', and this dormancy decay is related to a decline in ABA content and sensitivity in seeds after imbibition. In this study, we aimed at investigating the effect of after-ripening on ABA signaling in barley, our cereal model species. Phosphosignaling networks in barley grains were investigated by a large-scale analysis of phosphopeptides to examine potential changes in response pathways to after-ripening. We used freshly harvested (FH) and after-ripened (AR) barley grains which showed different ABA sensitivity. A total of 1,730 phosphopeptides were identified in barley embryos isolated from half-cut grains. A comparative analysis showed that 329 and 235 phosphopeptides were upregulated or downregulated, respectively after ABA treatment, and phosphopeptides profiles were quite different between FH and AR embryos. These results were supported by peptide motif analysis which suggested that different sets of protein kinases are active in FH and AR grains. Furthermore, in vitro phosphorylation assays confirmed that some phosphopeptides were phosphorylated by SnRK2s, which are major protein kinases involved in ABA signaling. Taken together, our results revealed very distinctive phosphosignaling networks in FH and AR embryos of barley, and suggested that the after-ripening of barley grains is associated with differential regulation of phosphosignaling pathways leading to a decay of ABA signaling.
脱落酸（ABA）是一种植物激素，是植物种子休眠的主要决定因素。种子在干燥储存过程中会逐渐失去休眠，这个过程被称为“后熟”，而这种休眠的衰减与种子吸胀后 ABA 含量和敏感性的下降有关。在这项研究中，我们旨在研究后熟对大麦中 ABA 信号的影响，大麦是我们的谷类模式物种。通过大规模分析磷酸肽来研究大麦谷物中磷酸化信号网络，以检查对后熟的反应途径的潜在变化。我们使用了新鲜收获（FH）和后熟（AR）的大麦种子，它们表现出不同的 ABA 敏感性。从半切谷物中分离出的大麦胚中鉴定出了 1730 种磷酸肽。比较分析表明，ABA 处理后分别有 329 和 235 种磷酸肽上调或下调，FH 和 AR 胚胎之间的磷酸肽谱差异很大。肽基序分析支持了这一结果，该分析表明，FH 和 AR 谷物中有不同的蛋白激酶活性。此外，体外磷酸化实验证实，一些磷酸肽被 SnRK2 磷酸化，SnRK2 是参与 ABA 信号的主要蛋白激酶。总之，我们的研究结果揭示了大麦 FH 和 AR 胚胎中非常独特的磷酸化信号网络，并表明大麦谷物的后熟与磷酸化信号通路的差异调节有关，导致 ABA 信号的衰减。
