Drought inhibition of tillering in Festuca arundinacea associated with axillary bud development and strigolactone signaling

Drought stress inhibits tiller formation and growth, but the underlying mechanism is not well understood. Tiller development and lateral branch growth in monocot and dicot species respectively involve two stages: axillary bud initiation and subsequent outgrowth. The objective of this study was to investigate whether drought-inhibition of tiller growth is mainly due to the suppression of axillary bud initiation or subsequent outgrowth in perennial grass species and to determine whether drought-inhibition of tiller development and growth in grass species are associated with strigolactone (SL) accumulation and signaling. Seedlings with one fully-expanded leaf without axillary buds and those with three-fully expanded leaves and two axillary buds were grown in 20% polyethylene glycol (PEG) solution to induce drought stress. Plant height, number of leaves, axillary buds, tillers and length of axillary buds were monitored during 21 d of stress. Both axillary bud initiation and outgrowth were inhibited by drought stress, with outgrowth being more sensitive to drought stress. qRT-PCR analysis showed that expression level of genes involved in axillary bud activity was down-regulated at 14 d of drought stress while genes involved in axillary bud dormancy was up-regulated. Strigolactone (SL) content was elevated under drought stress in crowns. qRT-PCR analysis showed that expression level of genes involved in SL biosynthesis and signaling transduction were up-regulated during drought stress. Axillary bud outgrowth was sensitive to drought stress and could be associated with SL signaling, contributing to drought-inhibition of tillering in perennial grass species.