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Article|14 Mar 2022|OPEN
Mitogen-activated protein kinase 4 is obligatory for late pollen and early fruit development in tomato
Jie Wang1,2 ,† , Mengzhuo Li1 ,† , Shibin Zhuo1 , Yue Liu1 , Xiaolin Yu1 , Sidra Mukhtar3 and Muhammad Ali1 , , Gang Lu,1,4 ,
1Department of Horticulture, Zhejiang University, Hangzhou 310058, China
2Ningbo Academy of Agricultural Sciences, Ningbo 315000, Zhejiang, China
3Directorate of Agriculture Research, Agricultural Research Institute Tarnab, Peshawar, Pakistan
4Key Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Ministry of Agricultural, Zhejiang University, Hangzhou 310058, China
*Corresponding author. E-mail: maur202@zju.edu.cn,glu@zju.edu.cn
Both authors contributed equally to the study.

Horticulture Research 9,
Article number: uhac048 (2022)
doi: https://doi.org/10.1093/hr/uhac048
Views: 17

Received: 25 Oct 2021
Accepted: 14 Feb 2022
Published online: 14 Mar 2022

Abstract

Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules regulating vegetative and reproductive development of plants. However, the molecular mechanisms of the SlMPK4 gene in tomato pollen and fruit development remain elusive. SlMPK4 is preferentially and highly expressed in tomato stamens and its mRNA levels increase during early flower development, peaking at the mature pollen stage. Either up- or downregulation of SlMPK4 expression had no significant effect on tomato vegetative growth. However, RNAi-mediated suppression of SlMPK4 caused defects in pollen development, resulting in pollen abortion. The aborted pollen grains were either malformed or collapsed and completely lacked viability, resulting in a predominantly reduced fruit set rate in RNAi lines compared with control and overexpressing transgenic plants. Interestingly, seed development was inhibited in RNAi lines. Moreover, >12% of emasculated RNAi flowers developed seedless fruits without pollination. Anthers can produce typical microspore mother cells as well as uninucleate microspores, according to cytological investigations, while binucleate pollen ceased to produce typical mature pollen. Pollen abortion was further confirmed by transmission electron microscopy analysis at the binucleate stage in RNAi plants. The exine layer in aberrant pollen had a normal structure, while the intine layer appeared thicker. Suppression of SlMPK4 affects the transcript level of genes related to cell wall formation and modification, cell signal transduction, and metabolic and biosynthetic processes. A subset of genes that may be putative substrates of plant MAPKs were also differentially changed in RNAi transgenic flowers. Taken together, these results suggest that SlMPK4 plays a critical role in regulating pollen development and fruit development in tomato plants.