三种藓类植物固碳耗水节律调节作用

Rhythmic regulation of carbon fixation and water dissipation in three mosses

藓类植物作为缺乏维管组织的非等水植物,其光合作用和耗水量主要受到光照、温度和水分供应状况的影响;这些环境条件随昼夜交替改变,是否使得藓类植物形成了类似维管植物的内在昼夜节律调节机制,目前还所知甚少;理解其节律响应特点对于藓类植物的保育与利用具有重要意义。该研究对脆枝青藓(Brachythecium thraustum)、大灰藓(Hypnum plumaeforme)和长叶提灯藓(Mnium lycopodioides)进行12 h/12 h的昼夜光周期驯化后进行24 h/0 h的持续光照处理,分别测定3种藓类在12 h/12 h和24 h/0 h光周期条件下的净光合速率(Pn)和蒸腾速率(Tr),结果表明:排除光照和叶-气水汽压差(VPD)等环境影响之后,3种藓类的这两个指标均观察到明显的节律变化,节律调节作用能够解释其Pn和Tr日变化的23.4%和30.2%;且维管植物中少见的Tr节律作用出现在所有受试的藓类植物上;Pn和Tr的节律响应存在明显的种间差异,该研究中节律性最强的物种为脆枝青藓。以脆枝青藓为例进一步分析其全光照下非结构性碳水化合物(NSC)的节律响应时序转录组,结果表明:35.1%的淀粉、糖类合成代谢相关基因的表达具有节律性,且与NSC含量的昼夜节律变化相关;脱落酸信号和气孔调节相关基因的表达变化与Tr的节律调节相关;光合电子传递和暗反应相关蛋白的转录水平变化与光合作用节律保持一致。藓类植物虽然丢失了生物钟核心反馈环CCA1/LHY基因,但是核心生物钟功能集中于PRRs家族,通过级联调节使得光合作用生物学过程和保卫细胞水分/离子运输过程等相关基因表达呈现显著的节律性,最终导致固碳耗水的节律响应高度保守。

Aims As anisohydric plants lacking vascular tissue,mosses are thought to be influenced on their water movement and photosynthesis mainly by the water status and light of the ambient environment.Do the mosses develop an intrinsic circadian regulation mechanism similar to that of vascular plants as these environmental conditions change with day and night alteration?Understanding its rhythmic response characteristics is of great significance for the conservation and utilization of the mosses.Methods The Brachythecium thraustum,Hypnum plumaeforme and Mnium lycopodioides were trained to 12 h/12 h light-dark(LD)cycles before transfer to 24 h/0 h constant light.We measured the three mosses’net photosynthetic rate(Pn)and transpiration rate(Tr)on the constant light and last day of the light-dark cycles.Subsequently,non-structural carbon(NSC)content was measured for Brachythecium thraustum.Finally,we sequenced the Brachythecium thraustum transcriptomes in a time series in constant light conditions.Important findings We found the significant rhythmic changes in the Pn and Tr of the three mosses when excluding environmental influences such as light and vapor pressure difference(VPD),and rhythmic regulation could explain 23.4% and 30.2% of the diurnal changes in Pn and Tr.Moreover,the rhythmic effect of Tr,which is rarely observed in vascular plants,appeared in all the mosses tested,and the rhythmic responses of Pn and Tr were different among species.The species with the strongest rhythm in this study was Brachythecium thraustum,and it was further analyzed for the rhythmic responses of time-series transcriptome and its NSC content under full light.The results showed that 35.1% of starch and carbohydrate biosynthesis-related genes showed rhythmic expression,which was closely related to NSC content change.In addition,the rhythmic regulation of Tr was associated with the transcript changes of abscisic acid signaling and stomatal regulation.Furthermore,the photosynthesis rhythms were associated with transcript changes of photosynthesis-related protein,like photosynthetic electron transport and carbon sequestration proteins.Although the CCA1/LHY genes,the core feedback loop of the circadian clock,have been lost in the mosses,the core circadian clock function concentrates in the PRRs family.The rhythmic response to carbon sequestration and water consumption is highly conserved.