OBV (obscure vein), a C2H2 zinc finger transcription factor, positively regulates chloroplast development and bundle sheath extension formation in tomato (Solanum lycopersicum) leaf veins

Jinghua Lu,Wenyue Su,Yongchen Du,Chunyang Pan,Feng Pan,Xiaoxiao Lu,Xin Li,Lei Liu,Xiaoxuan Wang,Zejun Huang,Min Zhang,Junling Hu,Yanmei Guo,Junming Li,Hui Zhang,Jinshuai Shu

doi:10.1038/s41438-021-00659-z

Abstract

Leaf veins play an important role in plant growth and development, and the bundle sheath (BS) is believed to greatly improve the photosynthetic efficiency of C4 plants. The OBV mutation in tomato (Solanum lycopersicum) results in dark veins and has been used widely in processing tomato varieties. However, physiological performance has difficulty explaining fitness in production. In this study, we confirmed that this mutation was caused by both the increased chlorophyll content and the absence of bundle sheath extension (BSE) in the veins. Using genome-wide association analysis and map-based cloning, we revealed that OBV encoded a C2H2L domain class transcription factor. It was localized in the nucleus and presented cell type-specific gene expression in the leaf veins. Furthermore, we verified the gene function by generating CRISPR/Cas9 knockout and overexpression mutants of the tomato gene. RNA sequencing analysis revealed that OBV was involved in regulating chloroplast development and photosynthesis, which greatly supported the change in chlorophyll content by mutation. Taken together, these findings demonstrated that OBV affected the growth and development of tomato by regulating chloroplast development in leaf veins. This study also provides a solid foundation to further decipher the mechanism of BSEs and to understand the evolution of photosynthesis in land plants.

Highlights

As the vascular system in leaves, leaf veins play a critical role in transporting water and nutrients to leaves, supporting the development of higher plants[1]
We employed the nearisogenic lines (NILs) IL5-4-5-44 and M82 to investigate the phenotype of the obv gene and several physiological traits
In IL5-4-5-44, the bundle sheath cells (BSCs) extended to the epidermis and formed bundle sheath extension (BSE), whereas no extension occurred in M82 (Fig. 1b)

Summary

Introduction

As the vascular system in leaves, leaf veins play a critical role in transporting water and nutrients to leaves, supporting the development of higher plants[1]. Bundle sheath cells (BSCs) form a wreath-like structure around the vasculature and connect the vascular bundle to the epidermis. The most important role for BSCs is to partition photosynthesis between the bundle sheath (BS) and mesophyll cells in C4 plants, improving the efficient fixation of CO2, under warm and dry conditions[4,5,6,7]. The BS of C3 plants is less important for photosynthesis than that of C4 species, it has a vital role in the control of hydraulic conductance[8], the transport of metabolites in and out of the veins[9], responses to high light episodes[10] and the assimilation of sulfur[11]

Methods

Results

Conclusion