中科院植生所植物分子遗传国家重点实验室林鸿宣研究员领导的研究组，在水稻重要性状遗传与功能基因研究上又取得重要进展。该研究组通过对水稻耐盐相关基因OsHAL3的功能分析，揭示了光调控植物发育的一个新机制。相关研究论文已于六月二十一日在线发表于国际著名学术杂志《自然-细胞生物学》(Nature Cell Biology)，并将刊登在7月份期的该杂志上。这是该研究组自2005年以来，继分离克隆水稻耐盐功能基因SKC1、水稻粒重功能基因GW2和水稻株型驯化基因PROG1之后，第四次将研究成果发表在Nature系列杂志上。
植物的生长速度和形态受到很多环境因子的影响，其中阳光是最为重要的一个因子。在弱光或黑暗的条件下，植物生长速度较快，形态幼嫩；而强光下则反之。这种现象对于植物适应光环境变化，完成生活史以及提高生物产量具有决定性的意义，因而一直以来是植物研究的基本问题之一。长期以来，传统的光受体调控机制是解释这一现象的主流模式。
HAL3(halotolerance3)是前人在筛选酵母耐盐基因的过程中分离克隆的抗逆相关基因，研究发现其编码一种促进细胞分裂以及提高耐盐性的核黄素蛋白。它的过量表达不仅可以提高植物的耐盐性，还可以加速植物的生长。林鸿宣研究员指导博士生孙世勇和晁代印等通过大量的实验，对水稻中HAL3同源基因OsHAL3开展了深入的功能和作用机理研究，发现这一基因介导了一个与普通光受体模式不同的光控发育机制。他们的研究证明，该基因编码的蛋白以三聚体的形式行使功能，而阳光，特别是蓝光可以促使三聚体解体，从而导致该蛋白功能失活；同时，光线还能抑制该基因的表达。光的这种双重抑制，使得细胞分裂减慢，最终导致水稻的生长变缓。他们的分析还表明，光照产生的活性氧以及光线对于HAL3配体FMN(flavin mononucleotide，黄素单核苷酸)的直接作用，可能是三聚体解聚的原因。进一步的试验显示，HAL3与一种可能参与降解细胞分裂抑制因子的E3泛素连接酶HIP1互作，并激活后者而促进细胞分裂。而先前发现的磷酸泛酰半胱氨酸脱羧酶的功能则被证明和其参与的细胞分裂作用不相关。这一结果也是第一次发现HAL3扮演细胞分裂信号传导的角色。同时，由于HAL3基因广泛存在于包括人类在内的生物界，使得这一研究具有更广泛的意义。
该研究得到国家科技部973项目、863专项、国家自然基金委和中科院知识创新工程等的资助。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature Cell Biology 21 June 2009 | doi:10.1038/ncb1892
OsHAL3 mediates a new pathway in the light-regulated growth of rice
Shi-Yong Sun1,4, Dai-Yin Chao1,4, Xin-Min Li1, Min Shi1, Ji-Ping Gao1, Mei-Zhen Zhu1, Hong-Quan Yang1, Sheng Luan2,3 & Hong-Xuan Lin1,2
Plants show distinct morphologies in different light conditions through a process called photomorphogenesis. A predominant feature of photomorphogenesis is the reduced growth of seedlings under light conditions compared with darkness. For this adaptive event, the most well-known molecular mechanism involves photoreceptor-mediated inhibition of cell elongation1, 2, 3, 4. However, it is not known whether additional pathways exist. Here, we describe a newly discovered pathway of light-modulated plant growth mediated by the halotolerance protein HAL3, a flavin mononucleotide (FMN)-binding protein involved in cell division5, 6, 7, 8. We found that light, especially blue light, suppresses growth of rice seedlings by reducing the activity of Oryza sativa (Os) HAL3. Both in vitro and in vivo studies showed that OsHAL3 is structurally inactivated by light through photo-oxidation and by direct interaction with photons. In addition, the transcriptional expression of OsHAL3 is synergistically regulated by different light conditions. Further investigation suggested that OsHAL3 promotes cell division by recruiting a ubiquitin system, rather than by its 4'-phosphopantothenoylcysteine (PPC) decarboxylase activity. Our results uncover a new mechanism for light-regulated plant growth, namely, light not only inhibits cell elongation but also suppresses cell division through HAL3 and E3 ubiquitin ligase. This study thus brings new insights into our understanding of plant photomorphogenesis.
1 National Key Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, 300 Fenglin Road, Shanghai 200032, China.
2 SIBS-UC Berkeley Center for Molecular Life Sciences, Shanghai Institutes for Biological Sciences (SIBS), Chinese Academy of Sciences, 300 Fenglin Road, Shanghai 200032, China.
3 Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA.
4 These authors contributed equally to this work.
