Molecular mechanisms controlling innate responses to injuries in plants

Abstract

All multicellular organisms experience various kinds of injuries during their growth. Repair and regrowth of lost body parts is a general phenomenon across the kingdoms. In animals, the repair mechanisms are lineage-specific, whereas, in plants, it is a universal phenomenon. The regeneration potential of plants can be attributed to their remarkable developmental plasticity. They respond to various biotic and abiotic insults by healing or re-growing the damaged parts. My work focuses on probing the mechanisms regulating innate regeneration responses to mechanical injuries in growing plant organs. For this, I have used the regeneration of specific cell types in wounded leaves as a model. Forty years ago, Tsvi Sachs, using his classical experiments using the aerial part of the stem, proposed the auxin canalization model for vein formation. How auxin is channelized and how local auxin accumulation repairs the loss remained elusive. While the ability to regenerate vascular tissue in the wounded stem is known for a long, it was believed that injured leaves cannot repair the wound. Contrary to this notion, I find that local injuries in growing leaves can be repaired without any support from artificial culture conditions. Vascular regeneration in leaves is highly sensitive to the size of the wound, the age of the plant, the position of injury and environmental conditions such as light. My studies led to the discovery of a feed-forward loop where genes encoding two distinct plant-specific transcription factors act coherently to increase local auxin production in the vicinity of the wound. This local hormonal environment sets up cell polarity and guides the path of reunion between physically disconnected veins. Interestingly, this regulatory module is required for vascular regeneration but not for vein formation during normal development. My studies distinguish the mechanisms between tissue regeneration and its normal developmental program. Unlike leaves growing in a normal developmental context, leaves detached from their plant body show a completely distinct regeneration. The cut end of the leaf can either heal the wound by local cell proliferation or can regenerate a completely new organ such as the root. This largely depends on whether the cut end of a leaf is in contact with the solid or liquid surface. Together, my studies provide a mechanistic framework of wound healing and tissue repair in response to mechanical injuries in aerial organs of plants.