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

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.

The impact of transposable elements on tomato diversity

“…1f and Supplementary Figure 1a). Notably, the Ty1/COPIA RIDER family, which generated insertion mutations with important agronomic implications 21,22,28,29 , contributes the highest number (507) of TIPs overall. Mobilome composition varies substantially among tomato groups and is richest in the genetically diverse SP group (~230 TE families, Fig.…”

A critical evaluation of the role of ethylene and MADS transcription factors in the network controlling fleshy fruit ripening

“…It has been shown to form a heterodimer with a second MADS-box protein JOINTLESS and regulate genes involved in pedicelspecific abscission processes including auxin/ethylene regulation, cell wall modifications, and production of several TFs involved in meristem maintenance and development . An additional MADS-box factor SlMBP21 also has been shown to form tetramers with MC and JOINTLESS and also is involved in abscission regulation (Roldan et al, 2017;Soyk et al, 2017). Tomato RIN might also be expected to act in concert with other MADS-box proteins.…”

Divergent Functional Diversification Patterns in the SEP/AGL6/AP1 MADS-Box Transcription Factor Superclade

“…Interestingly, more recent studies in tomato have elucidated the function of the enigmatic FBP9 subclade genes. It was found that SLMBP21/JOINTLESS2 (J2) is required for the development of the pedicel abscission zone (Liu et al, 2014;Roldan et al, 2017;Soyk et al, 2017). Furthermore, a breakthrough functional study (Soyk et al, 2017) based on both natural and CRISPR-Cas9 -induced mutant alleles showed that the two tomato FBP9 clade genes SLMBP21/J2 and SlMADS1/ENHANCER OF JOINTLESS2 (EJ2) have overlapping functions in meristem maturation and the control of inflorescence branching together with LONG INFLORESCENCE (LIN), the second tomato SEP4-like gene.…”

“…While the strongest phenotype was obtained in the tomato triple mutants, analysis of single and double mutants revealed also individual contributions to tomato development: LIN limits internode length and the number of flowers that develop per inflorescence, EJ2 negatively regulates sepal size, while both J2 and EJ2 are involved in the control of branching of the tomato inflorescence (Soyk et al, 2017). In addition, J2 is required for the development of the pedicel abscission zone (Liu et al, 2014;Roldan et al, 2017;Soyk et al, 2017).…”