Deciphering molecular mechanisms controlling seed development under low energy stress

摘要：种子产量是一项重要的农艺性状，取决于种子的正常发育。众所周知，包括胚胎发生在内的早期发育阶段在很大程度上受植物激素生长素介导的转录调控控制。此外，最近的研究表明，集中于能量剥夺的环境压力也只会干扰种子的早期建立，导致硅藻生长抑制和种子流产。尽管这种低能量胁迫（LES）响应的特征是根据植物的主要能量状态进行可逆和动态调整，但其潜在的分子机制尚不清楚。在我们之前的工作中，我们揭示了植物能量管理系统的核心参与者，即基本亮氨酸ZIPper 11 （bZIP11）相关转录因子（TF），它由关键的低能量激活Snf1相关蛋白激酶1 （SnRK1s）控制，将低能量相关刺激整合到生长素驱动的分生组织生长过程中。这在机制上是通过控制特定的Aux/IAAs的表达来实现的，这些Aux/IAAs构成生长素信号传导、生长素运输和生长素驱动的分生组织活性的负反馈调节器。由于bZIP的表达导致种子结实和bzip11相关转录物的显著减少，这些转录物是能量依赖性转录后调控的基础，揭示了早期胚珠内明显的积累，我们假设SnRK-bZIP生长调控系统根据植物的主要能量储备来调节生长素介导的种子发育。这种低能量触发系统在发育早期而不是后期运作，可以将剩余能量资源输送到接近完成的种子，从而确保植物后代在低能量状态下的存活。为了验证这一假设，我们将首先表征饥饿响应的bZIP表达域和胚胎发生过程中的动力学。在确定的、bZIP控制的种子阶段，我们将利用诱导和本构的功能增益和功能损失方法，研究bZIP错误表达对高能量和低能条件下胚胎生长素信号传导和形态的影响。获得的结果将揭示bzip11相关的TFs在饥饿响应种子发育中的影响。最后，我们将结合RNAseq和ChIPseq技术，通过破译bZIP调控子下游的转录网络来解决潜在的分子机制。综上所述，拟议的项目将提供能量饥饿如何转化为种子发育的基本见解。所获得的知识将有力地促进植物逆境适应过程的基础研究，并由于其对种子产量的影响，支持抗逆性作物的开发。

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.