Laboratory of Plant Breeding, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1, Gakuen-cho, Naka-ku, Sakai, Osaka, 599-8531, Japan.
Education and Research Field, School of Life and Environmental Sciences, Osaka Prefecture University, 1-1, Gakuen-cho, Naka-ku, Sakai, Osaka, 599-8531, Japan.
Planta. 2019 Nov;250(5):1557-1566. doi: 10.1007/s00425-019-03251-x. Epub 2019 Jul 29.
Morphological and genetic markers indicate that in sorghum, the juvenile-to-adult phase transition occurs during the fourth and fifth leaf stages. This timing differs from those reported for other plants. The juvenile-to-adult (JA) phase transition is an important event for optimizing vegetative growth and reproductive success in plants. Among the Poaceae crops, which are a vital food source for humans, studies of the JA phase transition have been restricted to rice and maize. We studied the morphological and genetic changes that occur during the early development of sorghum and found that dramatic changes occur in shoot architecture during the early vegetative stages. Changes were observed in leaf size, leaf shape, numbers of trichomes, and size of the shoot apical meristem. In particular, the length/width ratios of the leaf blades in the fifth and upper leaves were completely different from those of the second to fourth leaves. The fifth and upper leaves have trichomes on their adaxial sides, which were absent on the lower leaves. We also analyzed expression of two microRNAs that are known to be molecular markers of the JA phase transition and found that expression of miR156 was highest in the second to fourth leaves and then was gradually down-regulated, whereas miR172 expression followed the opposite pattern. These results suggest that in sorghum, the second and third leaves represent the juvenile phase, the fourth and fifth leaves are in the transition stage, and the sixth and upper leaves are in the adult phase. Thus, the JA phase transition occurs during the fourth and fifth leaf stages. These findings are expected to be useful for understanding the early development of sorghum.
形态和遗传标记表明，高粱的幼年期到成年期的转变发生在第四和第五叶期。这一时间与其他植物报道的时间不同。幼年期到成年期（JA）的转变是植物优化营养生长和生殖成功的重要事件。在禾本科作物中，这些作物是人类重要的食物来源，JA 转变的研究仅限于水稻和玉米。我们研究了高粱早期发育过程中发生的形态和遗传变化，发现在早期营养阶段，茎结构发生了剧烈变化。观察到叶片大小、叶片形状、毛状体数量和茎顶分生组织大小的变化。特别是，第五和上部叶片的叶片长宽比与第二至第四叶片完全不同。第五和上部叶片的腹侧有毛状体，而下部叶片没有。我们还分析了两个已知是 JA 转变的分子标记的 microRNA 的表达，发现 miR156 在第二至第四叶片中的表达最高，然后逐渐下调，而 miR172 的表达则相反。这些结果表明，在高粱中，第二和第三叶片代表幼年期，第四和第五叶片处于转变期，第六和上部叶片处于成年期。因此，JA 转变发生在第四和第五叶期。这些发现有望有助于理解高粱的早期发育。
