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

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.

Variation in the fruit development gene POINTED TIP regulates protuberance of tomato fruit tip

“…Additionally, as PT is part of a previously reported domestication sweep 34 , our results suggest that the mutation/phenotype likely hitch-hiked along with other loci sweeping through. A particular candidate for selection is the SP5G locus 31 , 35 . Meanwhile, we determined the PT H and PT R genotypes in 311 tomato accessions (Supplementary Data 1 ).…”

“…7 ). Coincidentally, recent research has identified the same SNP as underlying the obscure vein (obv) mutation and found that overexpression of OBV exhibited a change from the dark veins into a transparent phenotype 31 . Consistent with their observations, we also detected the phenotype of transparent veins in PT H -overexpressing plants as compared with the wild-type TS-9.…”

“…The obv mutant was first described as obvious variations in the vein in 1990 35 . Subsequently, several studies have suggested that the obv mutation may have “hitch-hiked” along with selection for mutations in the nearby SELF PRUNING 5 G ( SP5G ), which leads to more compact habits and shorter growing season 31 , 35 , 39 , 40 . Therefore, we propose that PT / OBV , may also have “hitch-hiked” along with the selection for mutations in the nearby SP5G .…”

“…A locus, designated as POINTED TIP ( PT ), is discovered and found to encode a C2H2 transcription factor. This locus has also been identified recently to underlie the “obscure vein” ( OBV ) 31 . A nucleotide substitution from A to G at the lead SNP generates two alleles of PT ( PT H and PT R ) that control the fruit blossom-end shape from a non-pointed tip to a pointed tip shape.…”

“…In Arabidopsis , KNUCKLES ( KNU ) might function as a transcriptional repressor of cellular proliferation that regulates floral determinacy and basal pattern elements because the knu mutant develops flowers and siliques with abnormal morphologies 26 . Previous studies have predicted 112 C2H2-type transcription factors in tomato 27 , and they have been implicated in multiple processes, such as ZF3 in salt tolerance 28 , Hair in trichome formation 29 , SE3.1 in flower development 30 , OBV in leaf veins development 31 . However, the natural variation of C2H2 zinc finger proteins and their influence on fruit shape in natural populations remains largely unknown.…”