DataSheet_1_Circadian clock does not play an essential role in daylength measurement for growth-phase transition in Marchantia polymorpha.docx

Daylength is perceived as a seasonal cue to induce growth-phase transition at a proper time of a year. The core of the mechanism of daylength measurement in angiosperms lies in the circadian clock-controlled expression of regulators of growth-phase transition. However, the roles of the circadian clock in daylength measurement in basal land plants remain largely unknown. In this study, we investigated the contribution of circadian clock to daylength measurement in a basal land plant, the liverwort Marchantia polymorpha. In M. polymorpha, transition from vegetative to reproductive phase under long-day conditions results in differentiation of sexual branches called gametangiophores which harbor gametangia. First, we showed that a widely used wild-type accession Takaragaike-1 is an obligate long-day plant with a critical daylength of about 10 hours and requires multiple long days. Then, we compared the timing of gametangiophore formation between wild type and circadian clock mutants in long-day and short-day conditions. Mutations in two clock genes, MpTIMING OF CAB EXPRESSION 1 and MpPSEUDO-RESPONSE REGULATOR, had no significant effects on the timing of gametangiophore formation. In addition, when M. polymorpha plants were treated with a chemical which lengthens circadian period, there was no significant effect on the timing of gametangiophore formation, either. We next observed the timing of gametangiophore formation under various non-24-h light/dark cycles to examine the effect of phase alteration in circadian rhythms. The results suggest that daylength measurement in M. polymorpha is based on the relative amount of light and darkness within a cycle rather than the intrinsic rhythms generated by circadian clock. Our findings suggest that M. polymorpha has a daylength measurement system which is different from that of angiosperms centered on the circadian clock function.

日照时长作为季节性信号，可诱导植物在一年中的适宜时段完成生长阶段转变。被子植物（angiosperms）的日照时长感知机制核心，在于受昼夜节律钟（circadian clock）调控的生长阶段转变调控因子的表达。然而，基部陆生植物（basal land plants）的昼夜节律钟在日照时长感知中所发挥的作用，目前仍未得到充分阐明。本研究以基部陆生植物地钱（Marchantia polymorpha）为对象，探究其昼夜节律钟在日照时长感知中的贡献。在地钱中，长日照条件下从营养生长向生殖生长的阶段转变，会分化出名为配子托（gametangiophores）的生殖枝，该结构承载配子囊（gametangia）。本研究首先证实，广泛使用的野生型品系Takaragaike-1为专性长日照植物，临界日长约为10小时，且需要经历多轮长日照周期方可完成阶段转变。随后，本研究在长日照与短日照条件下，对比了野生型与昼夜节律钟突变体的配子托形成时序。两个时钟基因MpTIMING OF CAB EXPRESSION 1与MpPSEUDO-RESPONSE REGULATOR的突变，均未对配子托形成时序产生显著影响。此外，当用可延长昼夜节律周期的化学试剂处理地钱植株时，配子托形成时序同样未出现显著变化。为探究昼夜节律相位改变的影响，本研究进一步在多种非24小时光暗循环条件下观察配子托形成的时序。结果表明，地钱的日照时长感知机制，是基于单个光暗循环内光照与黑暗的相对时长，而非由昼夜节律钟产生的内在节律。本研究结果显示，地钱所拥有的日照时长感知系统，与以昼夜节律钟功能为核心的被子植物感知系统存在显著差异。