多胺参与调控甜玉米发育过程中种子干重变化的分子机理研究

Poor seed quality is a serious impediment to the development of the sweet corn industry. Seed vigor is an important indicator of seed quality and is also the major component of seed value, and is closely related with the field emergence. Seed vigor is gradually formed during seed development, and will reach the highest value when seed is physiological maturity. However, the molecular mechanism of seed vigor formation is still a scientific problem to be solved. Seed weight had been reported as an important index to judge the level of the seed vigor, in addition, there is relatively close relationship between polyamines and seed vigor. Some studies showed that polyamines could improve seed germination capacity under adversity as well as seed development. Our preliminary studies also confirmed that polyamines played a significant role in the regulation of seed vigor formation during seed development of sweet corn. However, up to now, there is no systematic report on the molecular mechanisms of polyamines regulating seed vigor formation of sweet corn. Therefore, based on the results of preliminary extensive researches, the new RNA sequencing technology was used in present study to find the key genes involved in polyamine regulation on seed vigor, especially on seed dry weight of sweet corn. Using transgenic maize plants by overexpression and RNAi technology to study the gene function and gene networks. The findings will clarify the molecular mechanism of polyamines involved in seed vigor formation of sweet corn during seed development, and has important theoretical significance and applied potential.

种子质量低下严重阻碍了甜玉米产业的发展。种子活力是种子质量的重要指标，与种子田间出苗密切相关。种子活力随着种子发育逐渐形成，至生理成熟时达到最高，但种子活力形成的分子机理尚是亟待解决的科学难题。多项研究已表明种子重量可作为判断种子活力高低的关键性指标，而多胺与种子活力尤其种子干重的关系密切，多胺能够提高种子逆境发芽能力及促进种子发育。本课题组前期研究结果也证实多胺参与调控甜玉米发育过程中种子活力的形成，但至今尚未见有关多胺调控甜玉米种子活力形成的分子机理的系统研究报道。因此，本研究采用近年新兴的转录组测序（RNA Sequencing）技术，寻找多胺尤其是Spd参与调控甜玉米发育过程中与种子干重变化密切相关的特异基因，通过超表达及RNAi技术获得转基因玉米植株，研究基因功能及基因网络。研究结果将阐明多胺参与甜玉米种子发育过程中活力形成的分子机理，具有重要的理论意义和应用潜力。

种子质量低下严重阻碍了甜玉米产业的发展。种子活力是种子质量的重要指标，与种子田间出苗密切相关，但种子活力形成的分子机理尚是亟待解决的科学难题。本课题组前期研究结果已证实多胺参与调控甜玉米发育过程中种子活力的形成，但至今尚未见有关多胺调控甜玉米种子活力形成的分子机理的系统研究报道。因此，本研究采用转录组测序技术，寻找多胺尤其是亚精胺（Spd）参与调控甜玉米发育过程中与种子干重变化密切相关的特异基因，通过RNAi及遗传转化技术，研究基因表达特性和功能调控机理。主要研究结果如下：（1）外源Spd显著促进了甜玉米发育期间种子中直链淀粉的积累，增加种子干重，提高了种子活力，促进幼苗生长；（2）通过对不同发育阶段的甜玉米种子转录组的测序分析，发现在对照和Spd处理的2165个差异表达基因中，1434个基因上调表达，并筛选到Spd参与调控甜玉米种子发育过程中活力形成尤其种子干重变化的关键候选基因ZmGBSSI，该基因主要编码直链淀粉合成酶GBSSI；（3）外源Spd处理后种子中ZmGBSSI表达量、GBSS活性、直链淀粉含量及干物质积累的提高可能与其对种子内源Spd、ABA和蔗糖含量的促进，及对GA和葡萄糖含量的抑制密切相关。Spd对支链淀粉代谢相关酶活性和基因表达量没有显著的调控作用；（4）通过遗传转化技术，获得水稻同源基因OsGBSSI的突变株系OsgbssI。研究发现GBSSI沉默显著抑制了水稻种子的发育和种子活力，且经Spd处理后并未得到提高。同时，相比支链淀粉，直链淀粉含量及其在吸胀早期的分解速率对种子萌发和幼苗生长起着更为重要的作用。综上表明，Spd处理对种子发育及活力形成具有明显的促进作用，这与Spd对种子内源直链淀粉代谢的加强尤其对GBSSI的调控密切相关。该研究结果初步揭示了Spd参与甜玉米种子发育过程中活力形成的分子机理，对其他作物有借鉴作用，也将有利于在遗传上改良甜玉米种子质量，具有重要的理论意义和应用潜力。