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Nature Plants：拟南芥种子中决定种子大小的可移动蛋白TFL1

已有 4767 次阅读 2020-8-28 14:21 |个人分类:每日摘要|系统分类:论文交流

Mobile TERMINAL FLOWER1 determines seed size in Arabidopsis

第一作者：Bin Zhang

第一单位：新加坡国立大学

通讯作者：Hao Yu

Abstract

背景回顾：Seed size is a pivotal agronomic trait that links plant sexual reproduction and subsequent seedling establishment, and is affected by the timing of endosperm cellularization following endosperm proliferation after double fertilization.

提出问题：The molecular switch that controls the timing of endosperm cellularization has so far been largely unclear.

主要发现：Here, we report that the Arabidopsis TERMINAL FLOWER1 (TFL1) is a mobile regulator generated in the chalazal endosperm, and moves to the syncytial peripheral endosperm to mediate timely endosperm cellularization and seed size through stabilizing ABSCISIC ACID INSENSITIVE 5. We further show that Ras-related nuclear GTPases interact with TFL1 and regulate its trafficking to the syncytial peripheral endosperm.

结论：Our findings reveal TFL1 as an essential molecular switch for regulating endosperm cellularization and seed size. Generation of mobile TFL1 in the chalazal endosperm, which is close to maternal vascular tissues, could provide a hitherto-unknown means to control seed development by mother plants.

Fig 6e. A model depicting the regulation of seed size by the mobile TFL1 within the SPE.

In wild-type (WT) seeds, RAN proteins interact with TFL1 and are required for TFL1 transport from the chalazal endosperm (CZE) to SPE, where TFL1 stabilizes ABI5, thus mediating timely cellularization of the endosperm and seed size. In dominant-negative RAN2 (DN-ran2) or TFL1 loss-of-function mutant (tfl1-20) seeds, lack of TFL1 in the SPE promotes ABI5 degradation, thus delaying endosperm cellularization and generating large seeds. Green or red CZE represents TFL1 mRNA or protein expression in the CZE, respectively. In seeds, small circles in CZE or SPE represent nuclei.

摘要

种子大小是一个非常重要的农艺性状，其关联着植物的有性生殖与随后的实生苗生长，种子大小受到双受精后紧随胚乳增殖的胚乳细胞化时间点的影响。然而，有关控制植物胚乳细胞化时间点的分子开关至今也不清楚。本文中，作者报道了拟南芥中的TERMINAL FLOWER1（TFL1）是一个来自合点端胚乳的可移动调控因子，会移动到合胞体peripheral endosperm组织中，通过稳定ABI5蛋白来适时介导胚乳的细胞化及种子大小。作者进一步的研究显示Ras相关的GTP酶会与TFL1互作，并且调控TFL1蛋白到合胞体peripheral endosperm的运输。本文的研究揭示了TFL1是调控植物种子胚乳细胞化和种子大小的必要分子开关。靠近母本维管组织的合点端胚乳中产生可移动的TFL1蛋白，这为母本植物控制种子大小提供了一个迄今未知的调控方式。

p.s. 被子植物中，胚乳是双受精过程中一个精子与两个极核结合形成的三倍体，而胚乳的发育就起始于初生胚乳核的分裂，根据初生胚乳核分裂后是否形成细胞壁，被子植物的胚乳可以分为三种类型：核型胚乳、细胞型胚乳与沼生目型胚乳。

核型胚乳：初生胚乳核的分裂不伴随细胞壁的形成，当游离胚乳核达到一定的数量时，胚乳开始细胞化。

细胞型胚乳：从初生胚乳核开始，每次分裂都伴随着细胞壁的形成，胚乳始终以细胞的形式存在。

沼生目型胚乳：第一次分裂形成细胞壁，分为一个珠孔室（靠近珠孔端）和一个合点室（靠近合点端）。而后，珠孔室进行多次游离核分裂，后期细胞化；而合点室不分裂或进行少数几次分裂，一般保持游离核。

p.s. 拟南芥为核型胚乳，发育如下（cy: cytoplasm 细胞质；en: endosperm 胚乳；mp: micropylar region 珠孔；cv: central vacuole 中央液泡；cz: chalazal end 合点；MCE: micropylar endosperm 珠孔端胚乳；e: embryo 胚胎；PEN: peripheral endosperm；CZE: chalazal endosperm 合点端胚乳；alv: alveoli 胚囊；no: endosperm nodules 胚乳节；ce: cellular endosperm 细胞化胚乳；alc: aleurone-like cell 糊粉层细胞；me: mature embryo 成熟胚胎）