The miR157-SPL-CNR module acts upstream of bHLH101 to negatively regulate iron deficiency responses in tomato

Iron(Fe)homeostasis is critical for plant growth,development,and stress responses.Fe levels are tightly controlled by intricate regulatory networks in which transcription factors(TFs)play a central role.A series of basic helix-loop-helix(b HLH)TFs have been shown to contribute to Fe homeostasis,but the regulatory layers beyond b HLH TFs remain largely unclear.Here,we demonstrate that the SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE(SPL)TF Sl SPL-CNR negatively regulates Fe-deficiency responses in tomato(Solanum lycopersicum)roots.Fe deficiency rapidly repressed the expression of Sl SPL-CNR,and Fe deficiency responses were intensified in two clustered regularly interspaced palindromic repeats(CRISPR)/CRISPRassociated protein 9-generated Sl SPL-CNR knockout lines compared to the wild-type.Comparative transcriptome analysis identified 47 Fe deficiencyresponsive genes the expression of which is negatively regulated by Sl SPL-CNR,one of which,Slb HLH101,helps regulate Fe uptake genes.Sl SPLCNR localizes the nucleus and interacts with the GTAC and BOX 4(ATTAAT)motifs in the Slb HLH101 promoter to repress its expression.Inhibition of Sl SPL-CNR expression in response to Fe deficiency was well correlated with the expression of the micro RNA Slymi R157.Slymi R157-overexpressing tomato lines displayed enhanced Fe deficiency responses,as did Sl SPL-CNR loss-of-function mutants.We propose that the Slymi R157-Sl SPL-CNR module represents a novel pathway that acts upstream of Slb HLH101 to regulate Fe homeostasis in tomato roots.

桑树SPL转录因子家族全基因组鉴定及特征分析

SQUAMOSA启动子结合类蛋白质(SQUAMOSA promoter binding protein-like,SPL)是一类植物生长发育和应对胁迫相关的重要转录因子。利用生物信息学方法,从川桑(Morus notabilis)基因组中鉴定到15个SPL基因,进化分析将其归为8个聚类组,其具有保守的基因结构和氨基酸基序,在拟南芥和水稻中存在多个直系同源基因,预测到7个MnSPLs基因的表达受miR156/157调控,MnSPLs在桑树多个组织中检测到表达,其中6个基因在5类组织中均有较高表达量,部分基因主要在冬芽和雄花中有较高表达量,MnSPL基因存在组织表达特异性,在桑树生长发育过程中发挥重要作用。