Silencing SlMED18, tomato Mediator subunit 18 gene, restricts internode elongation and leaf expansion

Abstract

Mediator complex, a conserved multi-protein, is necessary for controlling RNA polymerase II (Pol II) transcription in eukaryotes. Given little is known about them in tomato, a tomato Mediator subunit 18 gene was isolated and named SlMED18. To further explore the function of SlMED18, the transgenic tomato plants targeting SlMED18 by RNAi-mediated gene silencing were generated. The SlMED18-RNAi lines exhibited multiple developmental defects, including smaller size and slower growth rate of plant and significantly smaller compound leaves. The contents of endogenous bioactive GA3 in SlMED18 silenced lines were slightly less than that in wild type. Furthermore, qRT-PCR analysis indicated that expression of gibberellins biosynthesis genes such as SlGACPS and SlGA20x2, auxin transport genes (PIN1, PIN4, LAX1 and LAX2) and several key regulators, KNOX1, KNOX2, PHAN and LANCEOLATE(LA), which involved in the leaf morphogenesis were significantly down-regulated in SlMED18-RNAi lines. These results illustrated that SlMED18 plays an essential role in regulating plant internode elongation and leaf expansion in tomato plants and it acts as a key positive regulator of gibberellins biosynthesis and signal transduction as well as auxin proper transport signalling. These findings are the basis for understanding the function of the individual Mediator subunits in tomato.

Developmental role of the tomato Mediator complex subunit MED18 in pollen ontogeny

“…In addition, vegetative developmental traits were also altered in pod1 mutant plants, mainly a significant reduction in fresh weight and leaf length compared with WT plants, as well as a decreased development of secondary and tertiary leaflets, and reduced length of petioles (Figure 1a; Table S1). Such alterations coincide with those reported by Wang et al (2018).…”

“…Recently, Wang et al . () have reported the function of tomato MED18 in regulating the development of leaf and stem. However, little is known about the role of MED18 in reproductive development.…”

“…In Arabidopsis, MED18 is involved in the transcriptional response to different physiological and cellular processes, like plant immunity (Lai et al, 2014), flowering time and floral organ identity (Zheng et al, 2013). Recently, Wang et al (2018) have reported the function of tomato MED18 in regulating the development of leaf and stem. However, little is known about the role of MED18 in reproductive development.…”

Specific functions for Mediator complex subunits from different modules in the transcriptional response of Arabidopsis thaliana to abiotic stress

“…These TFs have been implicated as central regulators of the low-energy transcriptional response which may overlap with the abiotic stress response 92 , and the data presented here implicate MED18 as a co-regulator during salt stress. bZIP11 and MED18 have both been implicated in auxin-mediated transcription, suggesting a possible integration point for these signaling pathways 93,94 . Our results also identify a putative interaction between MED18 and light signaling pathways via the PIF1/PIF3 TFs.…”

Mediator subunit OsMED14_1 plays an important role in rice development

“…Multifunctional property and specificity of Mediator subunits have also been illustrated by Lai et al (), where MED18 has been shown to affect diverse Arabidopsis functions through interaction with specific transcription factors. Notably, if its emerging role in Arabidopsis is put aside, the Mediator complex remains largely unexplored in other plants except for a few recent reports in tomato, sugarcane and wheat (Liu et al , ; Zhang et al , ; Pérez‐Martín et al , ; Wang et al , ). MED14 is one of the important Mediator subunits that has substantial transcriptional involvement in addition to playing a core architectural role through its interaction with different subunits across head, middle and tail Mediator modules (Cevher et al , ; Tsai et al , ; Robinson et al , ).…”