Towards a mechanistic understanding of global regulators of plant lifecycle transitions and seedling responses to environmental stresses

种子休眠的特征是分散的种子在通常有利于萌发的条件下暂时不能萌发。某些针叶树种(如黄柏)的种子在成熟时表现出明显的休眠，扩散时萌发能力低，需要几个月的潮湿冷藏来打破休眠。农业和林业依赖的种子发芽率高，萌发后活力旺盛，生长同步。然而，这些行业遇到了与种子质量差和持续休眠有关的问题。对于一些栽培物种来说，休眠通常被认为是一种不受欢迎的特征。黄柏是一种对加拿大非常重要的高海拔树种，其种子在秋季散布，对于黄柏来说，种子休眠是一种关键的适应特征，可以防止在寒冷的冬季发芽。我们已经定义了一些影响针叶树种子休眠和质量的机械因素，并开发了改进针叶树种子萌发和幼苗生长的工具。然而，我们最引人注目的发现是关于发芽抑制物脱落酸(ABA)的发现，以及一种名为ABI3的蛋白质，它有助于传递ABA信号。ABI3蛋白控制着许多对种子存活至关重要的事件。这包括食物储备的积累、休眠和种子组织对干燥的耐受性。最近，ABI3蛋白在其他植物组织的休眠中以及试图“抵御”环境压力(如极端高温和低温、高盐度和干旱)的幼苗中更广泛的作用变得明显。我们已经从黄柏中分离出ABI3基因(CnABI3)，并确定了该蛋白的部分功能。此外，我们还鉴定了三种与CnABI3相互作用的黄柏蛋白，并进一步发现CnABI3可能在开花调控中发挥作用。在树木和其他植物物种中，ABI3蛋白可能发挥全球调节作用，调节植物生命周期的所有关键转变。然而，这种蛋白质的多种功能的潜在机制还不完全清楚。这种理解的一部分将来自对CnABI3相互作用蛋白之一的详细描述，我们称之为“CnAIP2”。我们知道这种蛋白在植物生命周期的关键转变过程中也扮演着重要的角色，但它扮演着ABI3蛋白的“计数器”或拮抗剂的角色。该提案的总体目标是：(1)了解ABI3-CnAIP2蛋白作为关键植物生命周期转变的“守门人”的机制，并确定这两个全球调控因子在种子和幼苗生存过程以及生命周期决策中的作用。(2)解决长期寒冷作为调节生命周期决定(特别是种子萌发和开花能力)的关键环境信号之间有趣的相似之处。(3)了解ABI3蛋白及其反义蛋白如何帮助幼苗适应环境胁迫。拟议的研究具有巨大的潜力，可以对种子和幼苗存活的关键过程产生新的机械学见解，这将对林业和农业具有实际意义。我们将从进化的角度研究种子和幼苗存活的过程，以了解树木(裸子植物)和其他植物(被子植物)之间的联系。长期的研究将产生关于调控蛋白如何参与对气候和海拔适应至关重要的环境信号整合的信息。

Seed dormancy is characterized by a transient inability of the dispersed seed to germinate under conditions that are normally conducive to germination. The seeds of certain conifer species (e.g. yellow-cedar) develop pronounced dormancy at maturity, exhibiting a low capacity for germination upon dispersal, and requiring several months of moist chilling to break dormancy. The agricultural and forestry industries rely upon seeds that exhibit high germinability and vigorous, synchronous growth after germination. However, these industries encounter problems related to poor seed quality and persistent dormancy. For some cultivated species then, dormancy is often considered an undesirable trait. For yellow-cedar, a high elevation species of great importance to Canada, whose seeds are dispersed in the fall, seed dormancy represents a critical adaptive trait that prevents germination during the cold winter months. We have defined some of the mechanistic factors that underlie the dormancy and quality of conifer seeds, and have developed tools for improving conifer seed germination and seedling growth. However, our most striking discoveries are those concerning the germination inhibitor abscisic acid (ABA), and a protein called ABI3, which helps to relay ABA signals. ABI3 proteins control many events that are critical to seed survival. This includes the deposition of food reserves, dormancy imposition and the acquisition of a tolerance of seed tissues to desiccation. Recently more widespread roles for ABI3 proteins have become apparent – in the dormancy of other plant tissues – and in young seedlings attempting to “fend off” environmental stresses, like extreme heat and cold temperatures, high salinity and drought. We have isolated the ABI3 gene from yellow-cedar (CnABI3) and have defined some of the functions of this protein. In addition, we have identified three yellow-cedar proteins that interact with CnABI3, and further have made the exciting discovery that CnABI3 may play a role in the regulation of flowering. In trees and other plant species, the ABI3 protein may function as a global regulator, acting to regulate all key transitions of the plant lifecycle. However, the mechanisms underlying the multiple functions of this protein are not fully understood. Part of this understanding will come from detailed characterization of one of the interacting proteins of CnABI3 that we have called “CnAIP2”. We know that this protein also plays important roles during key transitions of the plant lifecycle, but it acts as a “counter” or antagonist to the ABI3 proteins. The overall objectives of this proposal are: (1) To understand the mechanisms by which ABI3-CnAIP2 proteins function as “gatekeepers” of key plant lifecycle transitions and define how the two global regulators act in seed and seedling survival processes, and in lifecycle decisions. (2) To address aspects of the interesting parallels between prolonged cold as a key environmental signal that regulates lifecycle decisions (especially seed germination and flowering competence). (3) To understand how the ABI3 proteins and their counter-proteins help young seedlings cope with environmental stresses. The proposed studies have great potential to yield novel mechanistic insights into processes critical to seed and seedling survival that will have practical implications for forestry and agriculture. We will look at the processes involved in seed and seedling survival from an evolutionary point of view to understand connections between trees (gymnosperms) and other plants (angiosperms). Long-term research will generate information about how the regulatory proteins may participate in the integration of environmental signals of importance to climatic and altitudinal adaptation.