Researchers YUMOTO Genki



Center for Ecological Research, Kyoto University


Kudoh Group

Research Fields
Plant molecular ecology
leaf senescence

Seasonally distinct controls of leaf senescence in response to self-shading and sink demand in Arabidopsis helleri

Leaves are the central organ of photosynthetic production, but they have other multiple functions including storage and translocation of photosynthetic products, and defense. In a previous study on longevity of leaf cohorts (leaves with shared age) in the evergreen perennial Arabidopsis helleri, cohorts that emerged during the growing season from late Feb to Sep (GS cohorts) had short leaf longevity and successive leaf senescence, while cohorts that emerged during the overwintering season from Oct to early Feb (OW cohorts) had extended leaf longevity and withered synchronously at the reproductive season. Based on the observations we speculated that leaf longevity controls primarily maximize photosynthetic production and storage/reproductive translocation for the GS and OW cohorts, respectively.
Here, we conducted a series of field manipulation experiments to determine whether leaf senescence is controlled distinctively between the growing and overwintering seasons. The detailed analyses of the field data showed that GS cohorts had varied leaf longevity within the cohorts despite their short average leaf longevity, suggesting that the environmental variation at the individual leaf level was important. The OW cohorts withered synchronously at the reproduction irrespective of their leaf ages, and we speculated that senescence control at the individual leaf level became less important and reproductive demand at the whole plant level was the major determinant of leaf senescence for OW cohorts. Then we manipulated self-shading and sink demands by moving leaves and removing the reproductive organs, respectively, and compared responses between GS and OW leaves in their longevity as well as transcriptomes using RNA-Seq.
In the GS cohorts, we found that self-shading accelerated leaf senescence with increased expression of stress-induced genes and chlorophyll catabolic pathways. Removal of new leaves prolonged leaf longevity. Thus, the leaf longevity of GS cohorts was controlled by depending on leaf age and local shading that determine photosynthetic efficiency to replace low efficient leaves by new leaves. In contrast, in the OW cohorts, leaf longevity was prolonged and became insensitive to shading, but leaf senescence was strongly suppressed by the removal of the reproductive organs. The expression of senescence genes induced by abiotic stress as well as ORE1 and NAP homologs was suppressed by sink-removal. The synchronous leaf senescence in the OW cohorts is achieved by the combination of shut-down of age- and shade-induced senescence and translocation of nutrients to the strong demand for reproduction at the whole plant level.
In conclusion, our results demonstrate that there is a major switching leaf senescence controls that optimize photosynthetic production and storage/reproductive translocation in the seasonal schedule of the perennial plant.

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