[植物生理] 生長素調節根部通氣組織的發育。 20191101 PNAS

Fine control of aerenchyma and lateral root development through AUX/IAA- and ARF-dependent auxin signaling

Takaki Yamauchi, Akihiro Tanaka, Hiroki Inahashi, Naoko K. Nishizawa, Nobuhiro Tsutsumi, Yoshiaki Inukai, and Mikio Nakazono

Abstract

Lateral roots (LRs) are derived from a parental root and contribute to water and nutrient uptake from the soil. Auxin/indole-3-acetic acid protein (AUX/IAA; IAA) and auxin response factor (ARF)-mediated signaling are essential for LR formation. Lysigenous aerenchyma, a gas space created by cortical cell death, aids internal oxygen transport within plants. Rice (Oryza sativa) forms lysigenous aerenchyma constitutively under aerobic conditions and increases its formation under oxygen-deficient conditions; however, the molecular mechanisms regulating constitutive aerenchyma (CA) formation remain unclear. LR number is reduced by the dominant-negative effect of a mutated AUX/IAA protein in the iaa13 mutant. We found that CA formation is also reduced in iaa13. We have identified ARF19 as an interactor of IAA13 and identified a lateral organ boundary domain (LBD)-containing

protein (LBD1-8) as a target of ARF19. IAA13, ARF19, and LBD1-8 were highly expressed in the cortex and LR primordia, suggesting that these genes function in the initiation of CA and LR formation. Restoration of LBD1-8 expression recovered aerenchyma formation and partly recovered LR formation in the iaa13 background, in which LBD1-8 expression was reduced. An auxin transport inhibitor suppressed CA and LR formation, and a natural auxin stimulated CA formation in the presence of the auxin transport inhibitor. Our findings suggest that CA and LR formation are both regulated through AUX/IAA- and ARF-dependent auxin signaling. The initiation of CA formation lagged that of LR formation, which indicates that the formation of CA and LR are regulated differently by auxin signaling during root development in rice.

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經由 AUX/IAA 以及 ARF 所調節的生長素訊息，精細地控制了植物的通氣組織與側根的發育

摘要

側跟是經由主跟分支出來，主要幫助從土壤中攝取水分跟養分的系統。對於側跟的發育而言，經由AUX/IAA（生長素抑制蛋白）與ARF（生長素反應蛋白） 調節的生長素反應是必要的程序。經由分解周圍細胞而形成的通氣組織，主要是經由皮質細胞的凋亡來生成，是植物用來增進氣體交換所生成的空間。水稻在含氧的環境下，會持續的形成通氣組織，然而在氧氣缺乏的狀態下會增加通氣組織的量來促進氣體交換。然而，持續形成的通氣組織背後的分子機制，到目前為止仍然未知。在顯性抑制突變的AUX/IAA突變株 -iaa13 中，側跟的數量有減少。我們發現了iaa13中的通氣組織也同樣的有減少。在之前的研究中，我們報導過ARF19會與IAA13互動也鑑定出一個包含LBD區域的蛋白質LBD1-8為ARF19的下游目標基因。這三個基因（IAA13/ARF19/LBD1-8）都在皮質層與側根源基（側跟的起始組織）有很高的表現，顯示這些基因都可能在通氣組織與側跟起始時有作用。在iaa13的突變植物中（LBD1-8表現量有明顯降低），表現LBD1-8可以恢復通氣組織的行程以及部分側跟的形成能力。而生長素運輸的抑制劑可以抑制通氣組織以及側根的形成，以及抑制天然生長素誘導的通氣組織的生成。我們的研究暗示通緝組織和側跟的形成，都是經由AUX/IAA以及ARF所調控的生長素訊息傳遞。然而相較於側跟的生成，通氣組織開始形成的時間較晚，也表示在水稻根的發育中，生長素在調節通氣組織與側跟的生成上有不同的途徑。

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＊我們已知生長素參與在大多數的植物生長與發育中，然而，通氣組織是一個我從未接觸過的一個組織，更令我訝異的是，大多數與環境壓力相關的反應，常常是經由ABA（離層酸）來調節的。這篇文章提到了水稻在處理生長素以及接受到缺氧狀態時，會形成較多的通緝組織，顯示生長素也有可能是參與壓力反應的一個賀爾蒙。而另一個有趣的點是，就像大多數的生長素反應一樣，這一個小小分子如何在不同的位置（皮質層與周鞘）誘導不同的反應，而且時間點還不同，這細微的調控是經由什麼因子調節，非常的神秘有趣。