Su Tao, Wolf Sebastian, Han Mei, Zhao Hongbo, Wei Hongbin, Greiner Steffen, Rausch Thomas
Plant Molecular Physiology, Centre for Organismal Studies (COS), Heidelberg University, Im Neuenheimer Feld 360, Heidelberg, 69120, Germany.
Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9, Canada.
Plant Mol Biol. 2016 Jan;90(1-2):137-55. doi: 10.1007/s11103-015-0402-2. Epub 2015 Nov 6.
In higher plants, cell wall invertase (CWI) and vacuolar invertase (VI) are recognized as essential players in sugar metabolism and sugar signaling, thereby affecting source-sink interactions, plant development and responses to environmental cues. CWI and VI expression levels are transcriptionally controlled; however, both enzymes are also subject to posttranslational control by invertase inhibitor proteins. The physiological significances of inhibitor proteins during seed germination and early seedling development are not yet fully understood. Here, we demonstrate that the inhibitor isoform AtCIF1 impacted on seed germination and early seedling growth in Arabidopsis. The primary target of AtCIF1 was shown to be localized to the apoplast after expressing an AtCIF1 YFP-fusion construct in tobacco epidermis and transgenic Arabidopsis root. The analysis of expression patterns showed that AtCWI1 was co-expressed spatiotemporally with AtCIF1 within the early germinating seeds. Seed germination was observed to be accelerated independently of exogenous abscisic acid (ABA) in the AtCIF1 loss-of-function mutant cif1-1. This effect coincided with a drastic increase of CWI activity in cif1-1 mutant seeds by 24 h after the onset of germination, both in vitro and in planta. Accordingly, quantification of sugar content showed that hexose levels were significantly boosted in germinating seeds of the cif1-1 mutant. Further investigation of AtCIF1 overexpressors in Arabidopsis revealed a markedly suppressed CWI activity as well as delayed seed germination. Thus, we conclude that the posttranslational modulation of CWI activity by AtCIF1 helps to orchestrate seed germination and early seedling growth via fine-tuning sucrose hydrolysis and, possibly, sugar signaling.
在高等植物中，细胞壁转化酶（CWI）和液泡转化酶（VI）被认为是糖代谢和糖信号传导中的关键参与者，从而影响源 - 库相互作用、植物发育以及对环境信号的响应。CWI和VI的表达水平受转录调控；然而，这两种酶也受到转化酶抑制蛋白的翻译后调控。抑制蛋白在种子萌发和幼苗早期发育过程中的生理意义尚未完全明确。在此，我们证明抑制蛋白亚型AtCIF1对拟南芥种子萌发和幼苗早期生长有影响。在烟草表皮和转基因拟南芥根中表达AtCIF1 YFP融合构建体后，AtCIF1的主要作用靶点显示定位于质外体。表达模式分析表明，AtCWI1在早期萌发种子中与AtCIF1在时空上共表达。在AtCIF1功能缺失突变体cif1 - 1中，观察到种子萌发在不依赖外源脱落酸（ABA）的情况下加速。这种效应与cif1 - 1突变体种子在萌发开始后24小时，体外和体内CWI活性的急剧增加相一致。相应地，糖含量定量显示cif1 - 1突变体萌发种子中的己糖水平显著提高。对拟南芥中AtCIF1过表达体的进一步研究表明，CWI活性明显受到抑制，种子萌发也延迟。因此，我们得出结论，AtCIF1对CWI活性的翻译后调节通过微调蔗糖水解以及可能的糖信号传导，有助于协调种子萌发和幼苗早期生长。
