文部省 科学研究費補助金 新学術領域研究 植物発生ロジックの多元的開拓

PubMed ID 26925070 Pubmed 日付 2016//
タイトル Suppressor Screen and Phenotype Analyses Revealed an Emerging Role of the Monofunctional Peroxisomal Enoyl-CoA Hydratase 2 in Compensated Cell Enlargement.
ジャーナル Frontiers in plant science  2016//  7()  132 
著者 Katano Mana M,Takahashi Kazuki K,Hirano Tomonari T,Kazama Yusuke Y,Abe Tomoko T,Tsukaya Hirokazu H,Ferjani Ali A
抄録 Efficient use of seed nutrient reserves is crucial for germination and establishment of plant seedlings. Mobilizing seed oil reserves in Arabidopsis involves β-oxidation, the glyoxylate cycle, and gluconeogenesis, which provide essential energy and the carbon skeletons needed to sustain seedling growth until photoautotrophy is acquired. We demonstrated that H(+)-PPase activity is required for gluconeogenesis. Lack of H(+)-PPase in fugu5 mutants increases cytosolic pyrophosphate (PPi) levels, which partially reduces sucrose synthesis de novo and inhibits cell division. In contrast, post-mitotic cell expansion in cotyledons was unusually enhanced, a phenotype called compensation. Therefore, it appears that PPi inhibits several cellular functions, including cell cycling, to trigger compensated cell enlargement (CCE). Here, we mutagenized fugu5-1 seeds with (12)C(6+) heavy-ion irradiation and screened mutations that restrain CCE to gain insight into the genetic pathway(s) involved in CCE. We isolated A#3-1, in which cell size was severely reduced, but cell number remained similar to that of original fugu5-1. Moreover, cell number decreased in A#3-1 single mutant (A#3-1sm), similar to that of fugu5-1, but cell size was almost equal to that of the wild type. Surprisingly, A#3-1 mutation did not affect CCE in other compensation exhibiting mutant backgrounds, such as an3-4 and fugu2-1/fas1-6. Subsequent map-based cloning combined with genome sequencing and HRM curve analysis identified enoyl-CoA hydratase 2 (ECH2) as the causal gene of A#3-1. The above phenotypes were consistently observed in the ech2-1 allele and supplying sucrose restored the morphological and cellular phenotypes in fugu5-1, ech2-1, A#3-1sm, fugu5-1 ech2-1, and A#3-1; fugu5-1. Taken together, these results suggest that defects in either H(+)-PPase or ECH2 compromise cell proliferation due to defects in mobilizing seed storage lipids. In contrast, ECH2 alone likely promotes CCE during the post-mitotic cell expansion stage of cotyledon development, probably by converting indolebutyric acid to indole acetic acid.

 Putative role of Auxin in CCE

東京学芸大学自然科学系生命科学分野 Ferjani Ali研究室 Ferjani Ali  投稿日時[2016-03-02 19:25:03]

Control of size is a longstanding issue in developmental biology. More than a decade ago, we noticed that a decrease in the number of cells in a developing leaf can trigger an unusual increase in post-mitotic cell expansion activity and thus cell size, which we collectively called compensation (Tsukaya, 1998, 2002). In our previous studies we identified many compensation-exhibiting mutants, cloned, and functionally characterized their causal genes. This lead to the emergence of basic features of compensation. Nevertheless, our understanding of this phenomenon is limited to the "TRIGGERING" factors, but the link(s) between cell proliferation defects and enhanced post-mitotic cell expansion (or compensated cell enlargement, CCE) remain to be elucidated.

In the present study, we mutagenized fugu5-1 seeds with heavy-ion irradiation, and screened for mutations that either partially or totally restrain CCE. Importantly, we found that a mutation in the Peroxisomal Enoyl-CoA Hydratase 2 (ECH2) totally suppressed CCE in fugu5. Interestingly, as shown in this study, the ech2-1 mutation did not affect at all CCE in other compensation-exhibiting mutants, such as fasciata1-6 and angustifolia3-4. Based on our results, we suggest a working model for regulation of CCE in fugu5, where the dual functions of ECH2 (TAG mobilization and IBA-to-IAA conversion) likely play a key role in CCE in fugu5 background.

In brief, the major outcome of this study is that "AUXIN" might be a candidate molecule to answer some of our longstanding questions about CCE in fugu5.

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** Abbreviations: TAG: triacylglycerol; IBA: indolebutyric acid; IAA: indole acetic acid.