The onset of embryo maturation in Arabidopsis is determined by its developmental stage and does not depend on endosperm cellularization

First author: John P. O'Neill; Affiliations: Franklin & Marshall College (富兰克林·马歇尔学院): Lancaster, USA

Corresponding author: Pablo D. Jenik

Seeds are dormant and desiccated structures, filled with storage products to be used after germination. These properties are determined by the maturation program, which starts, in Arabidopsis thaliana, mid‐embryogenesis, at about the same time and developmental stage in all the seeds in a fruit. The two factors, chronological and developmental time, are closely entangled during seed development, so their relative contribution to the transition to maturation is not well understood. It is also unclear whether that transition is determined autonomously by each seed or whether it depends on signals from the fruit. The onset of maturation follows the cellularization of the endosperm, and it has been proposed that there exists a causal relationship between both processes. We explored all these issues by analyzing markers for maturation in Arabidopsis mutant seeds that develop at a slower pace, or where endosperm cellularization happens too early, too late, or not at all. Our data show that the developmental stage of the embryo is the key determinant of the initiation of maturation, and that each seed makes that transition autonomously. We also found that, in contrast with previous models, endosperm cellularization is not required for the onset of maturation, suggesting that this transition is independent of the hexose/sucrose ratio in the seed. Our observations indicate that the mechanisms that control endosperm cellularization, embryo growth, and embryo maturation act independently of each other.

种子是休眠和干燥的结构，里面充满着种子发芽后所需的营养物质。这些物质成分是胚胎成熟过程中积累的，在拟南芥中，也就是在胚胎发育的中期左右，同一个果实中所有种子都大概在同一时间点和发育时期起始该过程。在植物种子发育过程中，时序性和发育时间两个因素相互纠缠，很难区分开他们各自对于促进种子进入成熟阶段的作用。还有一点不清楚，就是在同一个果实中，不同种子是否能够自主性进入成熟阶段，还是得依赖于来自果实的信号。一般来说，植物种子的成熟是紧接着胚乳的细胞化发生的，所以有人提出胚乳的细胞化进程与种子进入成熟阶段肯定存在某种必然的联系。作者在一个种子发育十分缓慢以及三种胚乳细胞化发育不正常（分别是胚乳细胞化出现太早、太晚或者不发生）的拟南芥突变体中，通过分析成熟的标记分别研究了这些问题。本文的研究结果显示，胚胎的发育时期是种子是否进入成熟的关键决定因素，而且每个种子能够自主性完成进入成熟的转变。与之前的研究模型相反，作者还发现种子的成熟并不一定需要胚乳细胞化，说明种子是否能够进入成熟阶段并不依赖于己糖/蔗糖的比例。本文的研究结果揭示了在植物中，控制胚乳细胞化、胚胎生长以及胚胎成熟的机制是相互独立的。

通讯：Pablo D. Jenik (https://www.fandm.edu/pablo-jenik)

个人简介：1994年，阿根廷布宜诺斯艾利斯大学，学士； 2000年，耶鲁大学，博士。

研究方向：植物胚胎发育的模式建成以及成熟。

doi: https://doi.org/10.1111/tpj.14324

Journal: the plant journal

First Published: March 22, 2019