Asymmetric Auxin Distribution is Not Required to Establish Root Phototropism in Arabidopsis
Asymmetric Auxin Distribution is Not Required to Establish Root Phototropism in Arabidopsis
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DOI：
10.1093/pcp/pcy018
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发表时间：
2018-04-01
影响因子：
4.9
通讯作者：
Sakai, Tatsuya
中科院分区：
文献类型：
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作者：
Kimura, Taro;Haga, Ken;Sakai, Tatsuya
一种不对称的生长素分布模式被认为是种子植物热带反应的基础。然而，目前还不清楚这种模式是否是根的负向光性所必需的。我们在这里证明了不对称的生长素分布不是建立拟南芥向光性所必需的。我们对生长素报告基因的详细分析表明，生长素在根的照射侧积累，以响应由光致弯曲引起的附带重力刺激。此外，一个向无性突变体表现出通过增强光致反应来抑制这种积累。在此背景下，我们的药理学和遗传学分析表明，生长素的极性运输和生长素的生物合成对于根的向重力性的建立是关键的，但对于根的向光性来说并不是关键的，并且这些过程中的缺陷实际上增强了根的向光性反应。生长素反应因子双突变体ARF7 arf19和生长素受体突变体TIR1表现出根向光性曲线的轻微减少，这表明某些特定的ARF蛋白及其调节因子的转录调控至少部分参与了根向光性。然而，生长素拮抗剂PEO-IAA[α-(苯乙基-2-酮)-吲哚-3-乙酸]抑制了根的向重力性，增强了向光性，这表明TIR1/AFB生长素受体和ARF转录因子在向光性中的作用较小。综上所述，我们从目前的数据中得出结论，拟南芥根的向光性反应是由一种未知的机制诱导的，这种机制不需要生长素的不对称分布，Cholodny-Went假说可能不适用于根向光性。
An asymmetric auxin distribution pattern is assumed to underlie the tropic responses of seed plants. It is unclear, however, whether this pattern is required for root negative phototropism. We here demonstrate that asymmetric auxin distribution is not required to establish root phototropism in Arabidopsis. Our detailed analyses of auxin reporter genes indicate that auxin accumulates on the irradiated side of roots in response to an incidental gravitropic stimulus caused by phototropic bending. Further, an agravitropic mutant showed a suppression of this accumulation with an enhancement of the phototropic response. In this context, our pharmacological and genetic analyses revealed that both polar auxin transport and auxin biosynthesis are critical for the establishment of root gravitropism, but not for root phototropism, and that defects in these processes actually enhance phototropic responses in roots. The auxin response factor double mutant arf7 arf19 and the auxin receptor mutant tir1 showed a slight reduction in phototropic curvatures in roots, suggesting that the transcriptional regulation by some specific ARF proteins and their regulators is at least partly involved in root phototropism. However, the auxin antagonist PEO-IAA [alpha-(phenylethyl-2-one)-indole-3-acetic acid] suppressed root gravitropism and enhanced root phototropism, suggesting that the TIR1/AFB auxin receptors and ARF transcriptional factors play minor roles in root phototropism. Taken together, we conclude from our current data that the phototropic response in Arabidopsis roots is induced by an unknown mechanism that does not require asymmetric auxin distribution and that the Cholodny-Went hypothesis probably does not apply to root phototropism.