Tanaka Ayumi, Ito Hisashi
Institute of Low Temperature Science, Hokkaido University, N19 W8, Sapporo, Hokkaido, 060-0819 Japan.
Plant Cell Physiol. 2025 Feb 28;66(2):139-152. doi: 10.1093/pcp/pcae093.
Research on chlorophyll degradation has progressed significantly in recent decades. In the 1990s, the structure of linear tetrapyrrole, which is unambiguously a chlorophyll degradation product, was determined. From the 2000s until the 2010s, the major enzymes involved in chlorophyll degradation were identified, and the pheophorbide a oxygenase/phyllobilin pathway was established. This degradation pathway encompasses several steps: (i) initial conversion of chlorophyll b to 7-hydroxymethyl chlorophyll a, (ii) conversion of 7-hydroxymethyl chlorophyll a to chlorophyll a, (iii) dechelation of chlorophyll a to pheophytin a, (iv) dephytylation of pheophytin a to pheophorbide a, (v) opening of the macrocycle to yield a red chlorophyll catabolite (RCC) and (vi) conversion of RCC to phyllobilins. This pathway converts potentially harmful chlorophyll into safe molecules of phyllobilins, which are stored in the central vacuole of terrestrial plants. The expression of chlorophyll-degrading enzymes is mediated by various transcription factors and influenced by light conditions, stress and plant hormones. Chlorophyll degradation is differently regulated in different organs and developmental stages of plants. The initiation of chlorophyll degradation induces the further expression of chlorophyll-degrading enzymes, resulting in the acceleration of chlorophyll degradation. Chlorophyll degradation was initially considered the last reaction in senescence; however, chlorophyll degradation plays crucial roles in enhancing senescence, degrading chlorophyll-protein complexes, forming photosystem II and maintaining seed quality. Therefore, controlling chlorophyll degradation has important agricultural applications.
近几十年来，叶绿素降解的研究取得了显著进展。在20世纪90年代，明确作为叶绿素降解产物的线性四吡咯结构得以确定。从21世纪初到2010年代，参与叶绿素降解的主要酶被鉴定出来，脱镁叶绿酸a加氧酶/叶胆色素途径得以确立。这条降解途径包括几个步骤：(i)叶绿素b最初转化为7-羟甲基叶绿素a，(ii)7-羟甲基叶绿素a转化为叶绿素a，(iii)叶绿素a脱螯合形成脱镁叶绿素a，(iv)脱镁叶绿素a脱植基形成脱镁叶绿酸a，(v)大环打开产生红色叶绿素分解产物(RCC)，以及(vi)RCC转化为叶胆色素。这条途径将潜在有害的叶绿素转化为安全的叶胆色素分子，这些分子储存在陆生植物的中央液泡中。叶绿素降解酶的表达由各种转录因子介导，并受光照条件、胁迫和植物激素的影响。叶绿素降解在植物的不同器官和发育阶段受到不同的调控。叶绿素降解的启动诱导叶绿素降解酶的进一步表达，导致叶绿素降解加速。叶绿素降解最初被认为是衰老中的最后反应；然而，叶绿素降解在增强衰老、降解叶绿素-蛋白质复合物、形成光系统II和维持种子质量方面发挥着关键作用。因此，控制叶绿素降解具有重要的农业应用价值。
