Russeting in Apple: Molecular Basis, Mechanism and Consequences

黄褐斑病是包括苹果在内的许多果树果实表面的一种重要病害。褐变是指周皮的形成。初级果皮上的微裂纹被认为是生锈的第一个明显迹象。然而，并不是所有的微裂纹都会导致锈蚀。微裂缝以某种方式触发周皮的形成，但这种触发的性质尚不清楚。我们建议的目标是：(1)详细描述黄褐斑形成过程中发生的解剖学和生物物理变化，并确定它们对果实表面屏障性质的影响；(2)在分子水平上确定导致黄褐斑形成的初始触发因素和事件序列。我们将结合使用解剖学、生物物理学和分子生物学的方法。我们的重点是皮肤解剖，角质层的微破裂，它与钉子形成的关系，以及可能导致应力集中的因素。解剖学数据作为发育的时间尺度，将与褐变过程中的物理和分子变化相关联。红褐色皮肤复合材料的生物物理性质包括对水和气体的渗透性和流变性。最后，分子研究将确定在(S)和诱导(S)周皮形成之前(S)和(S)的初始和主要触发因素。我们专注于裂果处理的水分诱导，因为(1)在果园条件下，这是引起锈病的最常见原因，(2)裂果系统允许直接比较同一水果上的锈果和非锈果表面。此外，还将考虑其他诱导方式(PGRs，机械伤害)，或自然发生的锈病(锈病与非锈病运动和品种)。它们用作区分主要信号/事件(紧张、膨胀等)的控件。来自次级信号/事件(角质合成下调、Suberin合成上调等)。产生的数据将有助于确定黄化的机理基础。更好地了解其原因是制定避免战略以最大限度地减少此类缺陷风险的先决条件。

Russeting is an important disorder of fruit surfaces of many fruit crops including apple. Russeting is the formation of a periderm. Microscopic cracks (microcracks) in the primary fruit skin are considered the first visible sign of russeting. However, not all microcracks result in russeting. Microcracks somehow trigger formation of a periderm, but the nature of this trigger is unknown. The objectives of our proposal are to (1)provide a detailed account of the anatomical and biophysical changes occurring during russet formation and to identify their consequences for the barrier properties of the fruit surface and (2) identify the initial trigger and sequence of events on a molecular level that result in russeting. We will use a combination of anatomical, biophysical and molecular approaches. We focus on skin anatomy, microcracking of the cuticle, its relationships with peg formation and factors potentially causing stress concentration. The anatomical data serve as a developmental time scale to which physical and molecular changes during russeting will be related. The biophysical properties of the russeting skin composite include its permeability to water and gas and its rheological properties. Finally, molecular studies will identify the initial and primary trigger(s) that precede(s) and induce(s) periderm formation. We focus on moisture induction of russeting using split fruit treatment because (1) under orchard conditions this is the most frequent cause of russeting and (2) the split fruit system allows to directly compare russeting and non-russeting surfaces on the same fruit. In addition, other modes of induction (PGRs, mechanical wounding), or naturally occurring russeting (russeting vs. non-russeting sports and cultivars) will be considered. They serve as a control to distinguish primary signals/ events (strain, turgor etc.) from secondary signals/events (downregulation of cutin synthesis, upregulation of suberin synthesis, etc.). The data generated will help to identify the mechanistic basis of russeting. A better understanding of its causes is a prerequisite to develop avoidance strategies to minimize the risk for such defects.