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发芽的条件下暂时不能发芽。某些针叶树种（如黄雪松）的种子在成熟时会产生明显的休眠，在传播时表现出较低的发芽能力，需要几个月的潮湿寒冷才能打破休眠。农业和林业工业依赖于种子，这些种子在发芽后表现出高发芽性和旺盛的同步生长。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，休眠通常被认为是一种不受欢迎的特性。对于黄雪松，一个高海拔物种非常重要的加拿大，其种子是分散在秋天，种子休眠是一个关键的适应特性，防止发芽在寒冷的冬季。我们已经确定了一些机械因素，休眠和针叶树种子的质量，并开发了工具，提高针叶树种子发芽和幼苗生长。然而，我们最引人注目的发现是关于发芽抑制剂脱落酸（阿坝）和一种名为ABI 3的蛋白质，它有助于传递阿坝信号。ABI 3蛋白控制许多对种子存活至关重要的事件。这包括食物储备的沉积、休眠的施加和种子组织对干燥的耐受性的获得。最近，ABI 3蛋白在其他植物组织的休眠中以及在试图“抵御”环境压力（如极端高温和低温、高盐度和干旱）的幼苗中的作用变得更加广泛。我们已经从黄杉中分离出ABI 3基因（CnABI 3），并确定了该蛋白的一些功能。此外，我们还鉴定了三种与CnABI 3相互作用的黄杉蛋白，并进一步发现CnABI 3可能在开花调控中发挥作用。在树木和其他植物物种中，ABI 3蛋白可能作为全局调节器发挥作用，调节植物生命周期的所有关键过渡。然而，这种蛋白质的多种功能的机制尚未完全了解。这种理解的一部分将来自CnAIP 3的相互作用蛋白之一的详细表征，我们称之为“CnAIP 2”。我们知道这种蛋白质在植物生命周期的关键转变中也起着重要作用，但它是ABI 3蛋白质的“计数器”或拮抗剂。本提案的总体目标是：（1）了解ABI 3-CnAIP 2蛋白作为关键植物生命周期转变的“看门人”的机制，并定义这两个全球调节器如何在种子和幼苗存活过程中以及生命周期决策中起作用。(2)解决长期寒冷作为调节生命周期决策（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ABI 3蛋白及其反蛋白如何帮助幼苗科普环境压力。拟议的研究有很大的潜力，产生新的机制的见解种子和幼苗生存的关键过程，将有实际意义的林业和农业。我们将从进化的角度来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。长期研究将产生有关调节蛋白如何参与整合对气候和海拔适应具有重要意义的环境信号的信息。

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.