Cytokinin is required for escape but not release from auxin mediated apical dominance.
Cytokinin is required for escape but not release from auxin mediated apical dominance.
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DOI：
10.1111/tpj.12862
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发表时间：
2015-06
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影响因子：
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通讯作者：
Leyser O
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文献类型：
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作者：
Müller D;Waldie T;Miyawaki K;To JP;Melnyk CW;Kieber JJ;Kakimoto T;Leyser O
生长素由活跃的初生茎尖产生，通过主茎向下运输，抑制其下腋芽的生长，形成根尖优势。在这里，我们利用拟南芥细胞分裂素（CK）的生物合成和信号突变体来探讨CK在这一过程中的作用。众所周知，CK促进了芽的生长，而生长素抑制了CK的合成，从而提出了一种假设，即从顶端优势地位的释放依赖于CK对芽的供应增加。我们的数据证实，斩首诱导茎中至少一个异戊烯基转移酶（IPT） CK生物合成基因的表达。我们进一步发现，CK应答型a型拟南芥应答调节（ARR）基因的一个分支的转录丰度在CK供应后在芽中增加，并且，与它们作为CK信号抑制剂的典型作用相反，这些基因是CK介导的芽激活所必需的。然而，对相关的arr和ipt多突变体的分析表明，芽CK反应的缺陷不影响生长素介导的芽抑制，并且ipt转录物水平的增加不需要在断头后释放芽。相反，我们的数据表明，CK可以克服生长素介导的芽抑制，使芽在有利条件下（如高硝酸盐可利用性）摆脱根尖优势。有人提出，从生长素介导的顶端优势中释放芽需要增加细胞分裂素的生物合成，从而增加芽的细胞分裂素供应。在这里，我们发现在拟南芥中，细胞分裂素的增加似乎对于从顶端优势释放芽是不必要的，而是允许芽摆脱顶端生长素的抑制作用，从而在有利的生长条件下促进芽的激活。
Auxin produced by an active primary shoot apex is transported down the main stem and inhibits the growth of the axillary buds below it, contributing to apical dominance. Here we use Arabidopsis thaliana cytokinin (CK) biosynthetic and signalling mutants to probe the role of CK in this process. It is well established that bud outgrowth is promoted by CK, and that CK synthesis is inhibited by auxin, leading to the hypothesis that release from apical dominance relies on an increased supply of CK to buds. Our data confirm that decapitation induces the expression of at least one ISOPENTENYLTRANSFERASE (IPT) CK biosynthetic gene in the stem. We further show that transcript abundance of a clade of the CK-responsive type-A Arabidopsis response regulator (ARR) genes increases in buds following CK supply, and that, contrary to their typical action as inhibitors of CK signalling, these genes are required for CK-mediated bud activation. However, analysis of the relevant arr and ipt multiple mutants demonstrates that defects in bud CK response do not affect auxin-mediated bud inhibition, and increased IPT transcript levels are not needed for bud release following decapitation. Instead, our data suggest that CK acts to overcome auxin-mediated bud inhibition, allowing buds to escape apical dominance under favourable conditions, such as high nitrate availability. It has been proposed that the release of buds from auxin-mediated apical dominance following decapitation requires increased cytokinin biosynthesis and consequent increases in cytokinin supply to buds. Here we show that in Arabidopsis, increases in cytokinin appear to be unnecessary for the release of buds from apical dominance, but rather allow buds to escape the inhibitory effect of apical auxin, thereby promoting bud activation in favourable growth conditions.