Autumn senescence - a transcriptional timetable

Autumn senescence - a transcriptional timetable

Autumn has finally arrived. Many of us are happy to meet cozy days, moments spent under the blanket while rain and cold are claiming up to our windows, enlightened by the candlelight, reading and enjoying apples with cinnamon, pumpkin spice, hot tea..or maybe we are an active person who enjoys spending time outside in long walks with dogs, observing beautiful colours of autumn leaves.

According to the annual timetable, the last week of September is the beginning of Autumn. This is just the early Autumn and only a few leaves are at the ground. Tree canopies are still green and we can start observing how they change into different shades of yellow, orange, red.

What happens behind visible processes?

Gene expressions in leaves present different colours because chlorophyll is going trough a degradation process. Plant pigment stays in its full potential needed for photosynthesis while the plant is surrounded with optimum conditions-light, warmth, water, nutrients/minerals content. When these conditions start to decline in early Autumn, we see the different expressions of colours in leaves, which are predetermined by genes. 

To follow autumn senescences, a team of researches developed genomic tools for model plants in the genus Populus (aspens and cottonwoods). Populus microarrays are made according to the large-scale expressed sequence tag sequencing programs (EST).

“On the basis of 36,354 Populus ESTs, obtained from seven cDNA libraries, we have created a DNA microarray consisting of 13,490 clones, spotted in duplicate. Of these clones, 12,376 (92%) were confirmed by resequencing and all sequences were annotated and functionally classified. Here we have used the microarray to study transcript abundance in leaves of a free-growing aspen tree (Populus tremula) in northern Sweden during natural autumn senescence. Of the 13,490 spotted clones, 3,792 represented genes with significant expression in all leaf samples from the seven studied dates. (1)

The energy in plants is declining due to mitochondrial inability to operate in its full potential and provide enough ATP for photosynthesis. Researches observed changes in gene expression which was followed by chlorophyll degradation and reflected a shift from photosynthetic competences to energy generation by mitochondrial respiration, oxidation of fatty acids and nutrient mobilisation. (1)

When compared with annual plants, model plants show increased transcriptional activity and activity of proteases right before changes in the leaf colour. According to these changes, researchers made a graph where we can see pigment colours and changes happening along with colder weather...

The end of September speeds up Autumn and soon will everything be colourful.." Winter is an etching, spring a watercolour, summer an oil painting and autumn a mosaic of them all."(Stanley Horowitz)

1) Anderson et all; "A transcriptional timetable of autumn senescence", (2004); MID: 15059257; PMCID: PMC395783; DOI: 10.1186/gb-2004-5-4-r24