Biology subjects

Fataftah, N.

Publications and source records attributed to Fataftah, N..

3 recordsLinked to original sources

bioRxiv2022

Timing Is Everything In Autumn - Coordination Of Senescence Onset By A Transcriptional Program In Response To Environmental And Phytohormone Signals

European aspen (Populus tremula L.) undergoes a coordinated senescence program during autumn; however, it is not known what exactly triggers it. To identify the cellular program leading to senescence, we utilized natural variation among Swedish aspen genotypes in a common garden to study senescence timing and the underlying changes in leaf phytohormone and transcriptome profiles. Apart from the patterns of major transcriptional cascade that was similar between the genotypes and closely associated with cytokinin and auxin metabolite levels and gradually decreasing air temperature during autumn, we detected patterns that consistently preceded or coincided with senescence onset in individual genotypes. Another cascade seemed to respond to short-term changes in weather conditions that re-wired the transcriptional network; the up-regulation of genes related to ethylene and abiotic stress, programmed cell death and translation occurred first in the early-senescing genotypes and later in the late one. Network analyses displayed a connection between the two cascades, metabolic stress and immunity responses mediated by salicylic acid (SA)-signalling pathway that was repressed along with SA levels at senescence onset. We propose that autumn senescence in aspen trees is affected by environmental variation that evokes stress and the timing is fine-tuned by their stress tolerance mechanism. One sentence summarySalicylic acid signalling pathway fine-tunes the timing of senescence onset under challenging environmental conditions in autumn.

plant biology↗

bioRxiv2021

Nitrate fertilization may delay autumn leaf senescence, while amino acid treatments do not

Fertilization with nitrogen (N)-rich compounds leads to increased growth, but may compromise phenology and winter survival of trees in boreal regions. During autumn, N is remobilized from senescing leaves and stored in other parts of the tree to be used in the next growing season. However, the mechanism behind the N fertilization effect on winter survival is not well understood and it is unclear how N levels or forms modulate autumn senescence. We performed fertilization experiments and showed that treating Populus saplings with high or low levels of inorganic nitrogen resulted in a delay in senescence. In addition, by using precise delivery of solutes into the xylem stream of Populus trees in their natural environment, we found that delay of autumn senescence was dependent on the form of N administered: inorganic N (NO3-1) delayed senescence but amino acids (Arg, Glu, Gln, and Leu) did not. Metabolite profiling of leaves showed that the levels of tricarboxylic acids (TCA), arginine catabolites (ammonium, ornithine), glycine, glycine-serine ratio and overall carbon-to-nitrogen (C/N) ratio were affected differently by the way of applying NO3-1 and Arg treatments. In addition, the onset of senescence did not coincide with soluble sugar accumulation in any of the treatments. Taken together, metabolomic rearrangement under different N forms or experimental setups could modulate senescence process, but not initiation and progression in Populus. We propose that the different regulation of C and N status through direct molecular signaling of NO3-1 could account for the contrasting effects of NO3-1 and Arg on senescence. One sentence summaryNitrate, administered by precision fertilization through injection into the trunk, may delay autumn senescence and change metabolism in Populus leaves, while the same amount of amino acids does not have the same effect.

plant biology↗

bioRxiv2021

GIGANTEA gene expression influence leaf senescence in Populus in two different ways

GIGANTEA (GI) genes have a central role in plant development and influence several processes such as light signaling, circadian rhythm and abiotic stress tolerance. Hybrid aspen T89 (Populus tremula x tremuloides) trees with low GI expression through RNAi have a severely compromised growth. In order to study the effect of reduced GI expression on leaf traits with special emphasis on leaf senescence, we grafted GI-RNAi scions onto wild type (WT) rootstocks and managed to restore scions growth. The RNAi line had distorted leaf shape and reduced photosynthesis, probably caused by modulating phloem or stomatal function, increased starch accumulation, higher carbon-to-nitrogen (C/N) ratio and a reduced capacity to withstand moderate light stress. GI-RNAi also induced senescence under long day (LD) and moderate light conditions. Furthermore, the GI-RNAi lines were affected in their capacity to respond to "autumn environmental cues" inducing senescence, a type of leaf senescence with characteristics different from senescence induced directly by stress under LD conditions. Whereas Overexpression of GI delayed senescence. The two different effects on leaf senescence were not affected by the expression of FT (Flowering locus T), were "local" - they followed the genotype of the branch independent on the position in the tree - and trees with modified gene expression grown in the field were affected in a similar way as under controlled conditions. Taken together, GI plays a central role to sense the environmental changes during autumn and determine the appropriate timing for leaf senescence in Populus. One sentence summaryLeaf senescence is a complex process that is not well understood, but this paper shows that changing the expression of one gene could influence leaf senescence in Populus trees in two separate ways.

plant biology↗