Transcriptional reprogramming during developmental and stress-induced leaf senescence in barley

Leaf function dynamically alters during development and in response to environmental cues, from being a source of assimilates in photosynthetically active leaves to a source of valuable resources in senescing leaves. Aim of this work was to investigate and compare reprogramming of gene expression in barley primary leaf at early and late stages of developmental and stress-induced senescence, specifically, senescence induced by drought (stop of irrigation) stress and nitrogen (N) deficiency (depletion of N-supply).

Reprogramming of gene expression was analyzed via microarray analyses.

Early stages of senescence were defined by a decrease in chlorophyll content by about 10 -20%, and later stages by a decrease in chlorophyll by about 50%. Developmental and drought-induced senescence resulted in about 1000 differentially regulated genes (DEGs) in early, and about 5000 DEGs in later stages. Despite of a similar decrease in chlorophyll content, low N treatment resulted in a much lower number of DEGs (100-500). At early stages, overlap in transcriptional reprogramming between the different conditions is low (at low N between 0.8 and 6.0 %, at drought between 0.3 and 37 %, at developmental senescence between 1.4 and 21 % of all DEGs) and most genes regulated are specific for the stress-condition. At later stages, specific pathways flow into a common senescence pathway which involves senescence-associated genes related to recycling of nutrients. In this stage overlap is much higher (at low N between 37 and 51 %, at drought between 3.9 and 79%, at developmental senescence between 4.3 and 86 % of all DEGs).

The data show that there is a hierarchical structure of the pathways leading to senescence. Knowledge about the structure and function of the complex, dynamic, environment-sensitive and highly flexible regulatory senescence-networks helps to identify key factors of plant performance under changing environment.