Abstract
Seedling establishment is a critical phase in the life of plants when they are the most vulnerable to environment. Growth arrest at post-germinative stage under stress is the major adaptive strategy to help germinating seedlings to survive a spectrum of stressful conditions. ABA signaling is the key pathway to control stress-induced developmental arrest. However, mechanisms controlling the phase transition under abiotic stress are not fully understood. Here, we described miR172b as a new key regulator controlling transition of germinating seedlings from heterotrophic to autotrophic growth under osmotic stress in Arabidopsis. We showed that miR172b and its target SNZ were co-expressed during early seedling development. Expression of miR172b and SNZ was low after radicle emergence and sharply increased at the checkpoint to autotrophic development under normal conditions. Interestingly, activation of miR172b and SNZ was completely abolished by ABA and osmotic stress. miR172b overexpression and snz-1 exhibited increased sensitivity to ABA and osmotic stress during specific post-germinative stage, and resulted in higher expression of ABI3, ABI5 and downstream genes, such as Em6 and RAB18, than wild type under ABA treatment. Our results revealed that miR172b is a critical regulator specifically controlling cotyledon greening during post-germinative growth by directly targeting SNZ under ABA treatment and osmotic stress.
Highlights
Seed germination, post-germinative growth and subsequent seedling establishment are central to successful stand establishment and population maintenance in plants, which are of great importance to agriculture and ecology [1]
After seed germination, germinating seedlings proceed through a critical developmental stage referred to as the transition from heterotrophic to autotrophic growth that can be tracked by cotyledon greening
As it has recently been shown that miR172 mediates post-germinative growth in Arabidopsis grown under normal conditions [13], we sought to determine whether miR172 may have a role in stress response and developmental checkpoint control under osmotic stress
Summary
Post-germinative growth and subsequent seedling establishment are central to successful stand establishment and population maintenance in plants, which are of great importance to agriculture and ecology [1]. Compelling evidence has shown that the checkpoint from heterotrophic to autotrophic development at the post-germinative stage is genetically controlled, and that this phase transition is highly vulnerable to various stresses including osmotic stress [2]. In order to prevent the adverse effects of environmental perturbations on the transition from post-germinative stage to subsequent seedling establishment, genetic and molecular mechanisms regulating adaptive response during the phase transition have evolved. It has been shown that ABA signaling plays key roles in both postgerminative growth arrest under stress and subsequent seedling establishment [1]. Activation of ABI3 and ABI5 is required for maintaining the germinating seedlings at the post-germinative stage (embryonic state) to survive periods of severe drought stress [10]
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