Hochmuth Anton, Carswell Matthew, Rowland Aaron, Scarbrough Danielle, Esch Lara, Kamble Nitin Uttam, Habig Jeffrey W, Seung David
John Innes Centre, Norwich Research Park, Norwich, NR4 7UH, UK.
Simplot Plant Sciences, J. R. Simplot Company, Boise, Idaho, 83707, USA.
Plant Biotechnol J. 2025 Feb;23(2):412-429. doi: 10.1111/pbi.14505. Epub 2024 Dec 10.
The molecular mechanisms underpinning the formation of the large, ellipsoidal starch granules of potato tuber are poorly understood. Here, we demonstrate the distinct effects of PROTEIN TARGETING TO STARCH2b (PTST2b) and MYOSIN RESEMBLING CHLOROPLAST PROTEIN (MRC) on tuber starch granule morphology. A gene duplication event in the Solanaceae resulted in two PTST2 paralogs (PTST2a and PTST2b). PTST2b is expressed in potato tubers, and unlike PTST2a, it had no detectable interaction with STARCH SYNTHASE 4. MRC expression was detectable in leaves, but not in tubers. Using transgenic potato lines in the variety Clearwater Russet, we demonstrate that MRC overexpression leads to the formation of granules with aberrant shapes, many of which arise from multiple initiation points. Silencing PTST2b led to the production of striking near-spherical granules, each arising from a single, central initiation point. Contrary to all reported PTST2 mutants in other species, we observed no change in the number of granules per cell in these lines, suggesting PTST2b is specifically involved in the control of starch granule shape. Starch content and tuber yield per plant were not affected by PTST2b silencing, but MRC overexpression led to strong decreases in both parameters. Notably, the spherical granules in PTST2b silencing lines had a distinctively altered pasting profile, with higher peak and final viscosity than the wild type. Thus, PTST2b and MRC are promising target genes for altering starch granule size and shape in potato tubers, and can be used to create novel starches with altered physicochemical and/or functional properties.
支撑马铃薯块茎中大型椭圆形淀粉粒形成的分子机制目前仍知之甚少。在此，我们展示了蛋白质靶向淀粉2b（PTST2b）和类肌球蛋白叶绿体蛋白（MRC）对块茎淀粉粒形态的不同影响。茄科植物中的一次基因复制事件产生了两个PTST2旁系同源基因（PTST2a和PTST2b）。PTST2b在马铃薯块茎中表达，与PTST2a不同，它与淀粉合酶4没有可检测到的相互作用。MRC在叶片中可检测到表达，但在块茎中未检测到。利用清水褐皮品种的转基因马铃薯株系，我们证明MRC过表达会导致形成形状异常的颗粒，其中许多颗粒源自多个起始点。沉默PTST2b会导致产生显著的近球形颗粒，每个颗粒都源自单个中央起始点。与其他物种中所有已报道的PTST2突变体相反，我们观察到这些株系中每个细胞的颗粒数量没有变化，这表明PTST2b特别参与淀粉粒形状的控制。淀粉含量和单株块茎产量不受PTST2b沉默的影响，但MRC过表达导致这两个参数大幅下降。值得注意的是，PTST2b沉默株系中的球形颗粒具有明显改变的糊化特性，其峰值粘度和最终粘度均高于野生型。因此，PTST2b和MRC是改变马铃薯块茎淀粉粒大小和形状的有前景的靶基因，可用于创造具有改变的物理化学和/或功能特性的新型淀粉。
