Abstract：
Strigolactones (SLs) are key regulators of shoot growth and responses to environmental stimuli. Numerous studies have indicated that nitrogen (N) limitation induces SL biosynthesis, suggesting that SLs may play a pivotal role in coordinating systemic responses to N availability, but this idea has not been clearly demonstrated. Here, we generated triple knockout mutants in the SL synthesis gene TaDWARF17 (TaD17) in bread wheat and investigated their phenotypic and transcriptional responses under N limitation, aiming to elucidate the role of SLs in the adaptation to N limitation. Tad17 mutants display typical SL mutant phenotypes, and fail to adapt their shoot growth appropriately to N. Despite exhibiting an increased tillering phenotype, Tad17 mutants continued to respond to N limitation by reducing tiller number, suggesting that SLs are not the sole regulators of tillering in response to N availability. RNA-seq analysis of basal nodes revealed that the loss of D17 significantly altered the transcriptional response of N-responsive genes, including changes in the expression profiles of key N response master regulators. Crucially, our findings suggest that SLs are required for the transcriptional downregulation of cytokinin (CK) synthesis and signalling in response to N limitation. Collectively, our results suggest that SLs are essential for the appropriate morphological and transcriptional adaptation to N limitation in wheat, and that the repressive effect of SLs on shoot growth is partly mediated by their repression of CK synthesis.
摘要：
Strigolactone（SL）是芽生长和对环境刺激的反应的关键调节剂。大量研究表明，氮（N）限制诱导SL生物合成，这表明SL可能在协调对N可用性的系统反应中发挥关键作用，但是这个想法还没有得到明确的证明。这里,我们在面包小麦中的SL合成基因TaDWARF17（TaD17）中产生了三重敲除突变体，并研究了它们在N限制下的表型和转录反应，旨在阐明SL在适应N限制中的作用。Tad17突变体显示典型的SL突变体表型，并且无法使其枝条生长适当地适应N。尽管表现出增加的分till表型，Tad17突变体继续通过减少分till数量来响应N限制，这表明SL并不是响应N可用性的分枝的唯一调节剂。对基底节点的RNA-seq分析表明，D17的丢失显着改变了N响应基因的转录反应，包括关键N响应主调节剂表达谱的变化。至关重要的是，我们的发现表明，SL是响应N限制的细胞分裂素（CK）合成和信号传导的转录下调所必需的。总的来说，我们的结果表明，SL对于小麦适当的形态和转录适应氮限制是必不可少的，SL对枝条生长的抑制作用部分是由其对CK合成的抑制作用介导的。
