Deciphering molecular mechanisms controlling seed development under low energy stress

低能量胁迫下种子发育的分子机制研究摘要：种子产量是一个主要的农艺性状，取决于种子的正常发育。众所周知，早期发育阶段，包括胚胎发生，在很大程度上是由植物激素生长素介导的转录调控控制。除此之外，最近的研究表明，集中在能量剥夺上的环境胁迫也专门干扰早期种子建立，导致角果的生长抑制和种子败育。虽然这种低能量胁迫（LES）响应的特征是根据植物的主要能量状态可逆地和动态地调节，但其潜在的分子机制尚不清楚。在我们以前的工作中，我们揭示了植物能量管理系统的核心参与者，即碱性亮氨酸ZIPper 11（bZIP 11）相关的转录因子（TF），由关键的低能量激活的Snf 1相关蛋白激酶1（SnRK 1）控制，将低能量相关刺激整合到生长素驱动的分生生长过程中。这是通过控制特定的Aux/IAA的表达来机械地实现的，Aux/IAA构成生长素信号传导、生长素运输和因此生长素驱动的分生组织活性的负反馈调节剂。由于bZIP表达被发现导致强烈减少的种子集和bZIP 11相关的转录本，其基础是能量依赖的转录后调节，揭示了早期胚珠内的明显积累，我们假设SnRK-bZIP生长调节系统进化为根据植物的主要能量储备来调节生长素介导的种子发育。具体操作在早期而不是晚期发育阶段，这种低能量触发系统可以使剩余的能量资源接近完成的种子通道，从而确保植物后代的生存下LES.To测试这一假设，我们将首先表征饥饿响应bZIP表达域和整个胚胎发生的动力学。在确定的bZIP控制的种子阶段，我们将研究bZIP错误表达对胚胎生长素信号传导和形态的影响，在高能量和低能量条件下，利用诱导型和组成型获得和丧失功能的方法。所获得的结果将揭示bZIP 11相关转录因子在饥饿响应种子发育中的影响。最后，我们将通过解密bZIP调节子下游的转录网络，应用RNAseq和ChIPseq技术的组合来解决潜在的分子机制。总的来说，拟议的项目将提供能量饥饿如何转化为种子发育的重要见解。所获得的知识将有力地促进植物胁迫适应过程的基础研究，并由于其对种子产量的影响，支持耐胁迫作物的发展。

Deciphering molecular mechanisms controlling seed development under low energy stressSummary:Seed yield is a major agronomic trait that depends on proper seed development. It is well-established that the early developmental stages, which comprise embryogenesis, are largely controlled by transcriptional regulation mediated by the phytohormone auxin. Besides this, recent studies revealed that environmental stresses that converge on energy deprivation, also exclusively interfere with early seed establishment, resulting in growth repression of siliques and seed abortion. Although this low energy stress (LES) response was characterised to be reversibly and dynamically tuned according to the plants` prevailing energy status, the underlying molecular mechanism is yet unknown.In our previous work, we unravelled that central players of the plant‘s energy management system, namely basic leucine ZIPper 11 (bZIP11) related transcription factors (TF), which are controlled by the pivotal low-energy activated Snf1 Related Protein Kinases 1 (SnRK1s) integrate low-energy related stimuli into auxin-driven meristematic growth processes. This is mechanistically accomplished by controlling expression of specific Aux/IAAs, which constitute negative feedback regulators of auxin signalling, auxin transport and in consequence auxin-driven meristem activity. As bZIP expression was found to result in strongly reduced seed set and bZIP11-related transcripts that underlie energy-dependent posttranscriptional regulation, reveal a distinct accumulation within the early ovule, we assume that a SnRK-bZIP growth regulatory system evolved to adjust auxin-mediated seed development according to the plants‘ prevailing energy reserves. Specifically operating during early and not late developmental stages, this low energy-triggered system could enable channelling of residual energy resources to nearly completed seeds, thereby ensuring survival of plant progeny under LES.To test this hypothesis, we will initially characterize starvation-responsive bZIP expression domains and kinetics throughout embryogenesis. At the defined, bZIP-controlled seed stages, we will study effects of bZIP mis-expression on the embryos’ auxin signalling and morphology under high- and low energy conditions, making use of inducible and constitutive gain- and loss-of-function approaches. The obtained results will unravel the impact of bZIP11-related TFs in starvation-responsive seed development. Finally, we will address the underlying molecular mechanisms by deciphering the transcriptional network downstream of the bZIP regulators, applying a combination of RNAseq and ChIPseq techniques. Taken together, the proposed project will provide essential insights how energy starvation is transduced into seed development. The obtained knowledge will strongly foster basic research on plant stress adaptation processes and, due to its impact on seed yield, support the development of stress tolerant crops.