Natural and induced loss of function mutations in SlMBP21 MADS-box gene led to jointless-2 phenotype in tomato

Maria Victoria Gomez Roldan,Samuel Huerga-Fernandez,Moussa Benhamed,David Latrasse,Halima Morin,Claire Périlleux,Abdelhafid Bendahmane

doi:10.1038/s41598-017-04556-1

Abstract

Abscission is the mechanism by which plants disconnect unfertilized flowers, ripe fruits, senescent or diseased organs from the plant. In tomato, pedicel abscission is an important agronomic factor that controls yield and post-harvest fruit quality. Two non-allelic mutations, jointless (j) and jointless-2 (j-2), controlling pedicel abscission zone formation have been documented but only j-2 has been extensively used in breeding. J was shown to encode a MADS-box protein. Using a combination of physical mapping and gene expression analysis we identified a positional candidate, Solyc12g038510, associated with j-2 phenotype. Targeted knockout of Solyc12g038510, using CRISPR/Cas9 system, validated our hypothesis. Solyc12g038510 encodes the MADS-box protein SlMBP21. Molecular analysis of j-2 natural variation revealed two independent loss-of-function mutants. The first results of an insertion of a Rider retrotransposable element. The second results of a stop codon mutation that leads to a truncated protein form. To bring new insights into the role of J and J-2 in abscission zone formation, we phenotyped the single and the double mutants and the engineered alleles. We showed that J is epistatic to J-2 and that the branched inflorescences and the leafy sepals observed in accessions harboring j-2 alleles are likely the consequences of linkage drags.

Highlights

Abscission is common in plants which thereby separate senescent or damaged organs from their main body, regulate fruit load and release ripe fruits for seed dispersal
Two allelic j-2 mutants (LA0315 and LA3899) were obtained from the Tomato Genetics Resource Center (TGRC). Both mutants are in determinate genetic backgrounds carrying a mutation in the SELF PRUNING (SP) gene: LA0315 is in Pearson (LA0012) background and LA3899, in addition of sp and j-2 mutations already described in its Ohio8245 parent[25], carries mutations B and u accounting for orange and uniform ripening fruits, respectively
Using the tomato genome sequence and transcriptomics data from flower pedicel abscission zone (AZ), we identified a candidate gene encoding a MADS-box protein

Summary

Introduction

Abscission is common in plants which thereby separate senescent or damaged organs from their main body, regulate fruit load and release ripe fruits for seed dispersal. The association of the lack of AZ with inflorescence and floral organ phenotypes in the j and mc mutants suggests that pedicel AZ formation may be an indirect effect of the genetic network regulating inflorescence architecture in tomato[7, 17]. Transcription factors that regulate meristem functions such as the tomato homolog of WUSHEL (LeWUS), GOBLET (GOB), LATERAL SUPPRESSOR (Ls) and Blind (Bl)[13, 18] were found associated with AZ formation. These data provided molecular support to the similarities between AZ layers at pre-abscission stage and meristematic cells and suggested an ancient signalling system to assure indeterminate cell maintenance in the AZ19

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Conclusion