Crawford Brian C W, Ditta Gary, Yanofsky Martin F
Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, CA 92093, USA.
Curr Biol. 2007 Jul 3;17(13):1101-8. doi: 10.1016/j.cub.2007.05.079.
The majority of pollen-tube growth in Arabidopsis occurs in specialized tissue called the transmitting tract. Little is currently known about how the transmitting tract functions because of a lack of mutants affecting its development. We have identified such a mutant and we used it to investigate aspects of pollen-tube growth.
Reverse genetics was used to identify mutations in a gene, No Transmitting Tract (NTT), encoding a C2H2/C2HC zinc finger transcription factor specifically expressed in the transmitting tract. The ntt mutants have a negative effect on transmitting-tract development. Stage-specific analysis of transmitting-tract development was carried out and was correlated with investigations of pollen-tube behavior. In ntt mutants, pollen tubes grow more slowly and/or terminate prematurely, and lateral divergence is accentuated over apical-to-basal movement. Normal transmitting-tract development is shown to involve a process of programmed cell death (PCD) that is facilitated by, but does not depend upon, pollination.
This is the first report of a gene that is specifically required for transmitting-tract development in Arabidopsis. Mutations in NTT cause reduced fertility by severely inhibiting pollen-tube movement. The data support the idea that the function of the transmitting tract is to increase fertilization efficiency, particularly in the lower half of the ovary. This occurs by facilitating pollen-tube growth through differentiation and then death of transmitting-tract cells.
拟南芥中大多数花粉管的生长发生在一种叫做传粉通道的特殊组织中。由于缺乏影响其发育的突变体，目前对传粉通道的功能了解甚少。我们已经鉴定出这样一个突变体，并利用它来研究花粉管生长的各个方面。
利用反向遗传学鉴定了一个名为“无传粉通道”（NTT）的基因中的突变，该基因编码一种在传粉通道中特异性表达的C2H2/C2HC锌指转录因子。ntt突变体对传粉通道的发育有负面影响。对传粉通道发育进行了阶段特异性分析，并与花粉管行为的研究相关联。在ntt突变体中，花粉管生长更缓慢和/或过早终止，并且侧向发散比顶端到基部的移动更明显。正常的传粉通道发育显示涉及程序性细胞死亡（PCD）过程，该过程由授粉促进，但不依赖于授粉。
这是关于拟南芥传粉通道发育特异性所需基因的首次报道。NTT中的突变通过严重抑制花粉管移动导致育性降低。数据支持这样的观点，即传粉通道的功能是提高受精效率，特别是在子房的下半部分。这是通过促进花粉管通过传粉通道细胞的分化然后死亡来生长而实现的。
