In plants, the process of aging, as well as many environmental constraints, may lead to the death of leaves. This particular type of cell death is often referred to as leaf senescence and can have a profoundly negative impact on crop yields and post-harvest shelf-life.
aim: Leaves are essential plant structures and their well-being is crucial for plant development and survival. When a stress is applied, a plant has two options: try to cope with it or induce senescence and reallocate valuable nutrients towards new, developing or storage organs. A mutual antagonistic relationship can summarize this phenomenon as shown in fig 1. Our aim is to understand how the plant validates senescence over an adaptation strategy in response to stress. This work mainly covers two aspects: 1) to unveil the communication and signalling mechanisms controlling the induction of leaf senescence and 2) to characterize the metabolic regulation that occurrs in response to stress and during leaf senescence.
1. Using dark-induced senescence as a proxy to decipher signalling pathways controlling the induction of leaf senescence
An individually-darkened leaf (IDL) for 6 days will undergo an accelerated senescence, whereas leaves from a plant entirely darkened (DP) for the same period of time will exhibit a sustained maintenance of their physiological functions and a subsequent repression of the process of senescence (Fig 2).
Great differences between transcriptomes and metabolomes of IDL and DP are observed, and highlight the different metabolic strategies between the two darkening treatment (Fig 3).
In order to identify the key players involved in the induction of senescence, we undertook a genetic screen allowing isolation of functional stay-green mutants. We are currently unveiling the function of these mutants.
2. Regulation of metabolism during leaf senescence
In a green leaf, the three energy organelles (peroxisome, mitochondrion and chloroplast) work in synergy to sustain an efficient assimilation of carbon while constantly maintaining the essential functions of the cell. However, when a leaf undergoes senescence ("yellowing"), whole cell-metabolism is drastically modified, and as chloroplasts are rapidly getting impaired, the remaining organelles acquire novel functions, particularly the mitochondrion. In animals, mitochondria have been shown to integrate various signals and to subsequently modulate cell death processes whereas in plants, the contribution of mitochondria in cell death regulation remains unclear, particularly during leaf senescence.
Therefore, we are currently investigating in more details the role of mitochondria during natural leaf senescence (i.e. aging).
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