一项为解决在水稻杂交稻制种中不育系的包穗问题提供了很好解决方案的研究成果，3月14日在《植物细胞》杂志在线发表。 

　　杂交水稻的发明和大规模应用不仅解决了中国人的吃饭问题，对世界减少饥饿也作出了卓越的贡献。杂交水稻的制种过程需要两个亲本材料——雄性不育系和恢复系，然而水稻不育系常常具有“包穗”的特性，为杂交稻制种带来很大困难。生产上往往需要在后期大量喷施“九二零”（赤霉素）来克服杂交制种中不育系的包穗问题。然而，“九二零”的施用不仅大大增加了制种成本、降低杂交种质量，而且其效果很大程度上取决于喷施者的技术、施用时期及天气状况等。水稻最上节间特异伸长突变体eui1的发现为育种家培育杂交水稻的高位茎节伸长不育系提供了可能，也大大简化了杂交稻的商业化制种。正是eui1具有解除不育系包穗的功效，因而，也被称为杂交水稻生产中除了不育系、保持系和恢复系外的第四遗传因子。 

　　2006年中科院遗传发育所储成才研究组和上海生科院何祖华研究组同时克隆了EUI1基因，发现EUI1编码一个细胞色素P450单加氧酶，可使具生物活性的赤霉素（促进细胞伸长的植物激素）失活。抑制EUI1表达可提高水稻内源赤霉素含量，从而增加其株高和穗颈长，但对EUI1表达调控机理一直以来并不清楚。 

　　中国科学院遗传发育所储成才研究组高少培博士进一步研究发现，HD-ZIP I类转录因子家族中的HOX12作为转录激活因子，可在植物体内与EUI1启动子直接结合并促进其表达，进而调控植物內源赤霉素的代谢和穗茎伸长。HOX12表达降低的植物中EUI1基因表达量也下降，活性赤霉素含量升高并从穗中向穗上部茎节中流动，导致穗茎中活性赤霉素含量增加，穗茎节变长。该项研究得到国家自然科学基金委和科技部转基因专项的资助。（来源：生物360） 

　　Rice HOX12 Regulates Panicle Exsertion by Directly Modulating the Expression of ELONGATED UPPERMOST INTERNODE1 

　　Abstract  Bioactive gibberellins (GAs) are key endogenous regulators of plant growth. Previous work identified ELONGATED UPPERMOST INTERNODE1 (EUI1) as a GA deactivating enzyme which plays an important role in panicle exsertion in rice (Oryza sativa). However, the mechanism that controls EUI1 activity during development is still largely unexplored. In this study, we identified a dominant panicle enclosure mutant regulator of eui1 (ree1-D), which is caused by the activation of a homeodomain-leucine zipper transcription factor HOX12. Diminished HOX12 expression by RNA interference enhances the panicle exsertion, mimicking the eui1 phenotype. Quantification of GA levels in the uppermost internodes revealed that the HOX12 knockdown plants contain higher levels of the major biologically active GAs (such as GA1 and GA4) than these in the wild type. The expression of EUI1 is elevated in the ree1-D mutant but lowered in HOX12 knockdown plants. Interestingly, both HOX12 and EUI1 genes are predominantly expressed in panicles, where GA4 is highly accumulated. Yeast one-hybrid, electrophoretic mobility shift assay, and chromatin immunoprecipitation analyses showed that HOX12 physically interacts with EUI1 promoter both in vitro and in vivo. Furthermore, overexpression of HOX12 in eui1 mutant background remains the elongated uppermost internode phenotype. These results reveal a novel regulatory module that HOX12 acts directly through EUI1 to regulate panicle exsertion in rice.