Division of Biological Sciences, University of Missouri Columbia, MO, USA ; Interdisciplinary Plant Group, University of Missouri Columbia, MO, USA ; Missouri Maize Center, University of Missouri Columbia, MO, USA.
Front Plant Sci. 2013 Jun 4;4:177. doi: 10.3389/fpls.2013.00177. eCollection 2013.
Recent developments have altered our view of molecular mechanisms that determine sink strength, defined here as the capacity of non-photosynthetic structures to compete for import of photoassimilates. We review new findings from diverse systems, including stems, seeds, flowers, and fruits. An important advance has been the identification of new transporters and facilitators with major roles in the accumulation and equilibration of sugars at a cellular level. Exactly where each exerts its effect varies among systems. Sugarcane and sweet sorghum stems, for example, both accumulate high levels of sucrose, but may do so via different paths. The distinction is central to strategies for targeted manipulation of sink strength using transporter genes, and shows the importance of system-specific analyses. Another major advance has been the identification of deep hypoxia as a feature of normal grain development. This means that molecular drivers of sink strength in endosperm operate in very low oxygen levels, and under metabolic conditions quite different than previously assumed. Successful enhancement of sink strength has nonetheless been achieved in grains by up-regulating genes for starch biosynthesis. Additionally, our understanding of sink strength is enhanced by awareness of the dual roles played by invertases (INVs), not only in sucrose metabolism, but also in production of the hexose sugar signals that regulate cell cycle and cell division programs. These contributions of INV to cell expansion and division prove to be vital for establishment of young sinks ranging from flowers to fruit. Since INV genes are themselves sugar-responsive "feast genes," they can mediate a feed-forward enhancement of sink strength when assimilates are abundant. Greater overall productivity and yield have thus been attained in key instances, indicating that even broader enhancements may be achievable as we discover the detailed molecular mechanisms that drive sink strength in diverse systems.
最近的发展改变了我们对决定源库强度的分子机制的看法，这里将源库强度定义为非光合结构竞争导入同化物的能力。我们综述了来自不同系统的新发现，包括茎、种子、花和果实。一个重要的进展是鉴定了新的转运蛋白和促进剂，它们在细胞水平上对糖的积累和平衡具有重要作用。每个转运蛋白的确切作用在不同的系统中有所不同。例如，甘蔗和甜高粱的茎都积累了高水平的蔗糖，但可能通过不同的途径来实现。这种区别对于使用转运蛋白基因有针对性地操纵源库强度的策略至关重要，也显示了系统特异性分析的重要性。另一个主要进展是将深层低氧确定为正常谷物发育的一个特征。这意味着胚乳中源库强度的分子驱动因素在非常低的氧水平下运作，并且在代谢条件下与之前假设的完全不同。然而，通过上调淀粉生物合成基因，仍然可以在谷物中成功增强源库强度。此外，我们对源库强度的认识因意识到蔗糖转化酶（INV）的双重作用而得到增强，不仅在蔗糖代谢中，而且在调节细胞周期和细胞分裂程序的六碳糖信号的产生中也有作用。这些 INV 对细胞扩张和分裂的贡献对于从花到果实的年轻源库的建立至关重要。由于 INV 基因本身就是对糖有反应的“盛宴基因”，当同化产物丰富时，它们可以介导源库强度的前馈增强。因此，在关键情况下实现了更高的整体生产力和产量，这表明，随着我们发现驱动不同系统源库强度的详细分子机制，甚至可以实现更广泛的增强。
