Epsilon Open Archive

Abstract

Of all of the organisms on the planet, trees are perhaps the ultimate survivors. Their unique growth characteristics allow them to become both the largest and the oldest organisms on Earth. Their size can be attributed to their secondary growth (wood formation), which results in the formation of their massive trunks, while their ability to survive and continue growing for several hundred years depends on their ability to modulate their growth according to the surrounding environment. This thesis explores wood formation and seasonal growth cycles on a molecular level. These tree-specific processes were studied separately, but several common factors that influence both of them were identified. One of these is the control of the core cell cycle machinery. The cell cycle machinery is subject to significant transcriptional regulation during the seasonal growth cycle; it was found that this transcriptional regulation primarily affects plant cyclins. A transcription factor of the AP2 family, AINTEGUMENTALIKE1 (AIL1), was shown to play a significant role in short-day- induced growth cessation, possibly by regulating the expression of the D-type cyclins, which are core regulators in the plant cell cycle. AIL1 is also involved in cambial growth; its misexpression causes severe developmental effects in the stem tissues. This thesis also provides new insights into the influence of the plant hormone auxin on tree growth and development. The known loss of auxin responsiveness during winter was shown to be a gradual process controlled by the intricate auxin signaling network. The same network was also studied during normal growth and shown to have a major influence on cambial activity and maintenance as well as wood development.