National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, 430070, China.
Microelement Research Centre, Huazhong Agricultural University, Wuhan, 430070, China.
Plant Cell Physiol. 2017 Nov 1;58(11):1991-2005. doi: 10.1093/pcp/pcx130.
Boron (B) is an essential micronutrient for the growth and development of plants. Oilseed rape (Brassica napus L.) is a staple oleaginous crop, which is greatly susceptible to B deficiency. Significant differences in tolerance of low-B stresses are observed in rapeseed genotypes, but the underlying mechanism remains unclear, particularly at the single-cell level. Here we provide novel insights into pectin-mediated cell wall (CW) mechanical properties implicated in the differential tolerance of low B in rapeseed genotypes. Under B deficiency, suspension cells of the low-B-sensitive genotype 'W10' showed more severely deformed morphology, lower viabilities and a more easily ruptured CW than those of the low-B-tolerant genotype 'QY10'. Cell rupture was attributed to the weakened CW mechanical strength detected by atomic force microscopy; the CW mechanical strength of 'QY10' was reduced by 13.6 and 17.4%, whereas that of 'W10' was reduced by 29.0 and 30.4% under 0.25 and 0.10 μM B conditions, respectively. The mechanical strength differences between 'QY10' and 'W10' were diminished after the removal of pectin. Further, 'W10' exhibited significantly higher pectin concentrations with much more rhamnogalacturonan II (RG-II) monomer, and also presented obviously higher mRNA abundances of pectin biosynthesis-related genes than 'QY10' under B deficiency. CW regeneration was more difficult for protoplasts of 'W10' than for those of 'QY10'. Taking the results together, we conclude that the variations in pectin-endowed CW mechanical properties play key roles in modulating the differential genotypic tolerance of rapeseed to low-B stresses at both the single-cell and the plant level, and this can potentially be used as a selection trait for low-B-tolerant rapeseed breeding.
硼（B）是植物生长和发育所必需的微量元素。油菜（Brassica napus L.）是一种主要的含油作物，对 B 缺乏非常敏感。油菜品种对低 B 胁迫的耐受性存在显著差异，但潜在机制尚不清楚，特别是在单细胞水平。在这里，我们提供了关于果胶介导的细胞壁（CW）机械性能在油菜品种对低 B 耐受性差异中的作用的新见解。在 B 缺乏的情况下，低 B 敏感基因型“W10”的悬浮细胞表现出更严重的变形形态、更低的活力和更容易破裂的 CW，而低 B 耐受基因型“QY10”则不然。细胞破裂归因于原子力显微镜检测到的 CW 机械强度减弱；在 0.25 和 0.10 μM B 条件下，“QY10”的 CW 机械强度分别降低了 13.6%和 17.4%，而“W10”的 CW 机械强度分别降低了 29.0%和 30.4%。在去除果胶后，“QY10”和“W10”之间的机械强度差异减小。此外，与“QY10”相比，“W10”在 B 缺乏条件下表现出明显更高的果胶浓度，具有更多的鼠李半乳糖醛酸聚糖 II（RG-II）单体，并且与果胶生物合成相关基因的 mRNA 丰度也明显更高。与“QY10”相比，“W10”的原生质体 CW 再生更困难。综合这些结果，我们得出结论，果胶赋予的 CW 机械性能的变化在调节油菜对低 B 胁迫的基因型差异耐受性方面起着关键作用，这可能被用作低 B 耐受油菜育种的选择性状。
