Flowering behaviour inArabis alpinaensures the maintenance of a perennating dormant bud bank

Abstract

22Arabis alpina, similar to woody perennials, has a complex architecture with a zone of axillary 23 vegetative branches and a zone of dormant buds that serve as perennating organs. We show that 24 floral development during vernalization is the key for shaping the dormant bud zone by 25 facilitating a synchronized and rapid growth after vernalization and thereby causing an increase 26 in auxin response and transport and endogenous indole-3-acetic acid (IAA) levels in the stem. 27 Floral development during vernalization is associated with the development of axillary buds in 28 subapical nodes. Our transcriptome analysis indicated that these buds are not dormant during 29 vernalization but only attain sustained growth after the return to warm temperatures. Floral and 30 subapical vegetative branches grow after vernalization and inhibit the development of the buds 31 below. Dormancy in these buds is regulated across the A. alpina life cycle by low temperatures 32 and by apical dominance in a BRANCHED 1-dependent mechanism. 35Bud dormancy plays an important role in survival through harsh environmental conditions and 36 long-term growth 1 . Thus, during the perennial life cycle, axillary and apical buds transition 37 through the various stages of dormancy before they resume active organogenesis and develop 38 into flowering or vegetative branches 2 . During development the outgrowth of axillary buds 39 close to the shoot apical meristem is repressed by apical dominance, a phenomenon also known 40 as correlative inhibition, latency or paradormancy, which occurs in both annual and perennial 41 species 3,4 . This form of dormancy is not definitive and paradormant buds can resume growth 42 when the main shoot apex is removed 5 . Buds in trees and herbaceous perennials also enter two 43 other forms of dormancy, endo-and eco-dormancy 2 . Endodormancy is regulated by 44 endogenous signals within the bud whereas ecodormancy is imposed by unfavorable 45 environmental conditions 6 . During the life cycle of a perennial plant, apical or axillary buds 46 experience winter in the endodormant state and later become ecodormant so that they will 47 actively grow only during favorable environmental conditions. It is however very common in 48 perennials for branches to have axillary buds during spring and summer, which later on will 49 stay dormant across multiple growing seasons. These dormant buds serve as a backup bud bank 50 and, in case of damage, are used as reservoirs for potential growth facilitating a bet-hedging 51 mechanism 7,8 . Interestingly, dormant buds and actively growing (vegetative or reproductive) 52 axillary branches are organized in zones in a species specific pattern 9,10 . 53The outgrowth of an axillary bud after decapitation involves two phases, firstly the rapid release 54 from dormancy and secondly its sustained growth 11 . Auxin, strigolactones, cytokinin and sugar 55 fine-tune this process by regulating the expression of the TCP transcription factor 56 BRANCHED 1 (BRC1) 12 . Decapitation causes an elev...