Tomato (Solanum lycopersicum) SlIPT4, encoding an isopentenyltransferase, is involved in leaf senescence and lycopene biosynthesis during fruit ripening

Abstract

BackgroundLycopene is an important carotenoid pigment in red fruits and vegetables, especially in tomato. Although lycopene biosynthesis and catabolism have been found to be regulated by multiple factors including phytohormones, little is known about their regulatory mechanism. Cytokinins are crucial to various aspects of plant growth. Isopentenyltransferases (IPTs) catalyze the initial rate-limiting step of cytokinins biosynthesis, however, their roles in fruit ripening remain unclear.ResultsHere, the functions of SlIPT4, encoding an isopentenyltransferase, were characterized via RNAi-mediated gene silencing in tomato. As we expected, silencing of SlIPT4 expression resulted in accelerated leaf senescence. However, down-expression of SlIPT4 generated never-red orange fruits, corresponding with a dramatic reduction of lycopene. Among lycopene biosynthesis-related genes, the fact of remarkable decrease of ZISO transcript and upregulation of other genes, revealed that SlIPT4 regulates positively lycopene biosynthesis via directly affecting ZISO expression, and also supported the existence of regulatory loops in lycopene biosynthesis pathway. Meanwhile, the accumulation of abscisic acid (ABA) was reduced and the transcripts PSY1 were increased in SlIPT4-RNAi fruits, supporting the feedback regulation between ABA and lycopene biosynthesis.ConclusionThe study revealed the crucial roles of SlIPT4 in leaf senescence and the regulatory network of lycopene biosynthesis in tomato, providing a new light on the lycopene biosynthesis and fruit ripening.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1327-0) contains supplementary material, which is available to authorized users.

A novel microRNA, SlymiR208, promotes leaf senescence via regulating cytokinin biosynthesis in tomato

“…In the present study, we report that a novel miRNA, named SlymiR208, is involved in tomato leaf senescence. SlymiR208 overexpression in tomato caused dramatic reduction of the target transcripts, SlIPT2 and SlIPT4 , and resulted in early leaf senescence, which was consistent with the phenotype of SlIPT4 ‐silenced lines described previously by us (Zhang et al 2018). Further, the levels of endogenous CKs were significantly decreased in SlymiR208 transgenic lines.…”

“…The genome DNA was erased and the first‐strand cDNA was synthesized using 2 μg of total RNAs by PrimeScriptRT reagent Kit with gDNA Eraser (Takara). The qPCR was performed using cDNA corresponding to 2 ng of total RNA in 10 μl reaction volumes using SYBR GREEN PCR Master Mix (Takara) on CFX96 Real‐Time System (Bio‐Rad) as previously described (Zhang et al 2018). For gene expression analysis, the oligo dT and Slactin51 (GenBank accession number Q96483) were used as reverse transcriptional primer and internal reference, respectively.…”

“…Genetic studies have proved that transgenic expression of IPT gene isolated from Agrobacterium tumefaciens increased the CK levels and delayed leaf senescence in tobacco (Gan and Amasino 1995), rice (Lin et al 2002), petunia (Chang et al 2003), maize (Robson et al 2004) and grass (Xu et al 2010). We recently reported that silencing of SlIPT4 expression in tomato resulted in early leaf senescence (Zhang et al 2018).…”

Transcriptome Analysis of Gene Expression Patterns Potentially Associated with Premature Senescence in Nicotiana tabacum L.

“…The upregulation of ABA2 in LA confirmed the increase of carotenoids and ABA. Additionally, PSY1 was also reported relative to ABA biosynthesis [ 36 ]. However, the expression profiles of PSY1 , CCD4, and D27 all exhibited down regulations, revealing the diversity of the molecular network between proteins and metabolites.…”

“…Some chlorophyll degradation-related genes (CDGs) were upregulated to accelerate the senescence induced by stresses and exogenous factors [ 31 , 32 , 33 ], Carotenoids serve as pigments, membrane stabilizers, and precursors of some plant hormones, functioning significantly in plant growth and response to abiotic stress [ 34 , 35 ]. It has been demonstrated that the silencing of SlIPT4 , which is encoding an isopentenyltransferase, resulted in the acceleration of leaf senescence [ 36 ]. Autophagy, which contributes to the remobilization of damaged cells interrupted by ROS [ 37 ], plays an important role in ageing senescence and stress-induced premature senescence [ 37 , 38 ].…”