植物从水生向陆生进化过程中，精细胞丧失了运动能力，需要依靠花粉管把它递送到雌配子体——胚囊中与卵子融合，完成受精。花粉管导向是一个精确调控的雌-雄配子体细胞相互识别的过程。胚囊释放吸引信号，花粉管接收信号后作出定向生长的反应。到目前为止，吸引信号已经被初步鉴定为一类分泌性质的小肽分子，但是花粉管对吸引信号的响应机制还是未知的。
中国科学院遗传与发育生物学研究所杨维才研究员带领的研究团队首次发现了一个控制花粉管响应的因子，命名为POD1。POD1同时控制花粉管响应和早期胚胎形态建成。通过遗传分析，结合亚细胞定位和转基因实验、细胞组分超速分离、酵母双杂交和荧光双分子互补等手段，该团队深入研究了POD1控制花粉管导向的分子机理。研究发现，POD1是一个定位在内质网腔中的蛋白，并与内质网中参与质量控制的关键因子钙网蛋白CRT3相互作用。并且，POD1控制内质网腔中含有HDEL定位信号的蛋白在内质网中的滞留。
这项工作首次揭示了内质网蛋白在花粉管响应过程中的关键作用，并为下一步分离其它控制花粉管响应的因子提供了新的切入点。这一工作表明，内质网蛋白在控制植物细胞-细胞间相互作用过程中可能是一个关键的控制节点。
上述研究结果于9月28日在线发表于国际杂志The Plant Cell。杨维才实验室的助研李红菊为该论文的第一作者。本研究得到了科技部重大研究计划项目和国家自然科学基金委的资助。
相关英文论文摘要：
POD1 Regulates Pollen Tube Guidance in Response to Micropylar Female Signaling and Acts in Early Embryo Patterning in Arabidopsis
The pollen tube germinates from pollen and, during its migration, it perceives and responds to guidance cues from maternal tissue and from the female gametophyte. The putative female cues have recently been identified, but how the pollen tube responds to these signals remains to be unveiled. In a genetic screen for male determinants of the pollen tube response, we identified the pollen defective in guidance1 (pod1) mutant, in which the pollen tubes fail to target the female gametophyte. POD1 encodes a conserved protein of unknown function and is essential for positioning and orienting the cell division plane during early embryo development. Here, we demonstrate that POD1 is an endoplasmic reticulum (ER) luminal protein involved in ER protein retention. Further analysis shows that POD1 interacts with the Ca2+ binding ER chaperone CALRETICULIN3 (CRT3), a protein in charge of folding of membrane receptors. We propose that POD1 modulates the activity of CRT3 or other ER resident factors to control the folding of proteins, such as membrane proteins in the ER. By this mechanism, POD1 may regulate the pollen tube response to signals from the female tissues during pollen tube guidance and early embryo patterning in Arabidopsis thaliana.
