Chloroplast division is a critical process for the maintenance of appropriate chloroplast number in plant cells. It is known that in some plant species and cell types, environmental stresses can affect chloroplast division, differentiation and morphology, however the significance and regulation of these processes are largely unknown. Here we investigated the regulation of salt stress-induced chloroplast division in protonemal cells of the moss, Physcomitrella patens, and found that, salt stress as one of the major abiotic stresses, induced chloroplast division and resulted in increased chloroplast numbers. We further identified three APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) transcription factors (TFs) that were responsible for this regulation. These AP2/ERF genes were up-regulated under salt stress, and amino acid sequences and phylogenetic analyses indicated that all TFs possess only one conserved AP2 domain and likely belong to the same subgroup of ERF-B3 in the AP2/ERF superfamily. Overexpression of these TFs significantly increased the chloroplast number even in the absence of NaCl stress. On the contrary, inducible overexpression of the dominant repressor form of these TFs suppressed salt stress-induced chloroplast division. Thus, our results suggest that salt stress induced-chloroplast division is regulated through members of the AP2/ERF TF superfamily.

叶绿体分裂是维持植物细胞中适当叶绿体数量的关键过程。众所周知，在某些植物物种和细胞类型中，环境胁迫会影响叶绿体的分裂，分化和形态，但是这些过程的意义和调控尚不清楚。在这里，我们研究了盐胁迫诱导的苔藓，小立碗藓原质细胞中叶绿体分裂的调节，并发现盐胁迫是主要的非生物胁迫之一，它诱导了叶绿体分裂并导致叶绿体数量增加。我们进一步确定了三个负责此调节的APETALA2 /乙烯响应因子（AP2 / ERF）转录因子（TFs）。这些AP2 / ERF基因在盐胁迫下上调，氨基酸序列和系统发育分析表明，所有TF仅具有一个保守的AP2结构域，可能属于AP2 / ERF超家族中的ERF-B3的同一亚组。这些TF的过表达即使在没有NaCl胁迫的情况下也显着增加了叶绿体数量。相反，这些TF的显性阻遏物形式的诱导型过表达抑制了盐胁迫诱导的叶绿体分裂。从而，