TCMP‐2 affects tomato flowering and interacts with BBX16, a homolog of the arabidopsis B‐box MiP1b

Abstract

Flowering and fruiting are processes subject to complex control by environmental and endogenous signals. Endogenous signals comprise, besides classical phytohormones, also signaling peptides and miniproteins. Tomato cystine‐knot miniproteins (TCMPs), which belong to a Solanaceous‐specific group of Cys‐rich protein family, have been recently involved in fruit development. TCMP‐1 and TCMP‐2 display a highly modulated expression pattern during flower and fruit development. A previous study reported that a change in the ratio of the two TCMPs affects the timing of fruit production. In this work, to investigate TCMP‐2 mode of action, we searched for its interacting partners. One of the interactors identified by a yeast two hybrid screen, was the B‐box domain‐containing protein 16 (SlBBX16), whose closest homolog is the Arabidopsis microProtein 1b implicated in flowering time control. We demonstrated the possibility for the two proteins to interact in vivo in tobacco epidermal cells. Arabidopsis plants ectopically overexpressing the TCMP‐2 exhibited an increased level of FLOWERING LOCUS T (FT) mRNA and anticipated flowering. Similarly, in previously generated transgenic tomato plants with increased TCMP‐2 expression in flower buds, we observed an augmented expression of SINGLE‐FLOWER TRUSS gene, the tomato ortholog of FT, whereas the expression of the antiflorigen SELF‐PRUNING was unchanged. Consistently, these transgenic plants showed alterations in the flowering pattern, with an accelerated termination of the sympodial units. Overall, our study reveals a novel function for TCMP‐2 as regulatory factor that might integrate, thanks to its capacity to interact with SlBBX16, into the signaling pathways that control flowering, and converge toward florigen regulation.

Beyond Arabidopsis: BBX Regulators in Crop Plants

“…Arabidopsis plants ectopically overexpressing the TCMP-2 exhibited an increased level of FLOWERING LOCUS T (FT) mRNA and anticipated flowering. Previously, the same authors revealed that transgenic tomato plants pTCMP-2::TCMP-1 with increased TCMP-2 expression in flower buds showed accelerated termination of the sympodial units [ 72 ]. In chrysanthemum, three B-box proteins have been identified so far that play a positive or negative role in regulating flowering time.…”

“…In chrysanthemum, three B-box proteins have been identified so far that play a positive or negative role in regulating flowering time. One of them, CmBBX8, stimulates flowering in summer-flowering chrysanthemum grown under LD conditions [ 71 ], while CmBBX13 and CmBBX24 proteins cause late flowering under long- and/or short-day conditions [ 64 , 65 , 66 , 70 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 ].…”

“… Involvement of B-box proteins as positive (blue) and negative (red) regulators of flowering in various crop plants including O. sativa : OsBBX5 (ID: Os02g0610500) [ 56 ], OsBBX7 (ID: Os02g0724000) [ 57 ], OsBBX10 (ID: Os03g0711100) [ 58 ], OsBBX14 (ID: Os05g0204600) [ 67 ], OsBBX17 (ID: Os06g0264200) [ 68 ], OsBBX18 (Os06g0275000) [ 55 ], OsBBX23 (ID: Os07g0667300) [ 59 ], OsBBX26 (ID: Os08g0536300) [ 60 ], OsBBX27 (ID: Os09g0240200) [ 69 ]; Z. mays : CONZ1 (ID: ABW82153) [ 61 ]; S. bicolor : SbCO (ID: Sb10g010050) [ 63 ]; C. morifolium : CmBBX24 (ID: KF385866) [ 64 ], CmBBX13 (ID: KP963935) [ 70 ], CmBBX8 (ID: KP96393) [ 71 ]; H. vulgare : HvCO1 (ID: AF490467) [ 65 ], HvCO9 (ID: AY082965) [ 66 ]; S. lycopersicum : SlBBX16 (ID: Solyc12g005750.1) [ 72 ]; S. tuberosum (ID: AM888389.1) [ 73 ]. LD—long day, SD—short day.…”

Overexpression of tomatoSlBBX16andSlBBX17impacts fruit development and gibberellin metabolism

“…Furthermore, Y2H analysis suggests that SlBBX17 and SlBBX16 share a common interacting partner, TCMP-2 (Figure S5B and Molesini et al 2020).…”

“…In this regard, Sl BBX16 was found to interact with the tomato cystine-knot peptide 2 (TCMP-2) (Molesini et al, 2020). TCMP-2 is specifically expressed in reproductive organs, its expression is low in pre-anthesis flower buds and gradually increases after fertilization, reaching a maximum in green and ripe fruits (Pear et al, 1989; Cavallini et al, 2011; Treggiari et al, 2015).…”