Tomato SlBL4 plays an important role in fruit pedicel organogenesis and abscission

Abstract

Abscission, a cell separation process, is an important trait that influences grain and fruit yield. We previously reported that BEL1-LIKE HOMEODOMAIN 4 ( SlBL4) is involved in chloroplast development and cell wall metabolism in tomato fruit. In the present study, we showed that silencing SlBL4 resulted in the enlargement and pre-abscission of the tomato (Solanum lycopersicum cv. Micro-TOM) fruit pedicel. The anatomic analysis showed the presence of more epidermal cell layers and no obvious abscission zone (AZ) in the SlBL4 RNAi lines compared with the wild-type plants. RNA-seq analysis indicated that the regulation of abscission by SlBL4 was associated with the altered abundance of genes related to key meristems, auxin transporters, signaling components, and cell wall metabolism. Furthermore, SlBL4 positively affected the auxin concentration in the abscission zone. A dual-luciferase reporter assay revealed that SlBL4 activated the transcription of the JOINTLESS, OVATE, PIN1, and LAX3 genes. We reported a novel function of SlBL4, which plays key roles in fruit pedicel organogenesis and abscission in tomatoes.

References

[1] Roberts, J. A., Elliott, K. A. & Gonzalez-Carranza, Z. H. Abscission, dehiscence, and other cell separation processes. Annu. Rev. Plant Biol. 53, 131-158 (2002).

[2] Addicot, F. T. Abscission (University of California Press, 1982).

[3] Taylor, J. E. & Whitelaw, C. A. Signals in abscission. N. Phytologist 151, 323-339 (2001).

[4] Bleecker, A. B. & Patterson, S. E. Last exit: senescence, abscission, and meristem arrest in Arabidopsis. Plant Cell 9, 1169-1179 (1997).

[5] McManus, M. T. Further examination of abscission zone cells as ethylene target cells in higherplants. Ann. Bot. 101, 285-292 (2008).

[6] Meir, S. et al. Identification of defense-related genes newly-associated with tomato flower abscission. Plant SignaBehavior 6, 590-593 (2011).

[7] Wang, X. et al. Transcriptome analysis of tomato flower pedicel tissues reveal abscission zone-specific modulation of key meristem activity genes. PLoS ONE 8, e55238 (2013).

[8] Roberts, J. A., Elliott, K. A. & Gonzalez-Carranza, Z. H. Abscission, dehiscence, andother cell separation processes. Annu. Rev. Plant Biol. 53, 131-158 (2002).

[9] Estornell, L. H., Agustí, J., Merelo, P., Talón, M. & Tadeo, F. R. Elucidating mechanisms underlying organ abscission. Plant Sci. 199-200, 48-60 (2013).

[10] Nakano, T., Fujisawa, M., Shima, Y. & Ito, Y. Expression profiling of tomato pre-abscission pedicels provides insights into abscission zone properties including competence to respond to abscission signals. BMC Plant Biol. 13, 1-19 (2013).

[11] Lashbrook, C. C., Tieman, D. M. & Klee, H. J. Differential regulation of the tomato ETR gene family throughout plant development. Plant J. 15, 243-252 (1998).

[12] Mao, L. et al. JOINTLESS is a MADS-box gene controlling tomato flower abscission zone development. Nature 406, 910-913 (2000).

[13] Budiman, M. A. et al. Localization of jointless-2 gene in the centromeric region of tomato chromosome 12 based on high resolution genetic and physical mapping. Theor. Appl. Genet. 108, 190-196 (2004).

[14] Nakano, T. et al. MACROCALYX and JOINTLESS interact in the transcriptional regulation of tomato fruit abscission zone development. Plant Physiol. 158, 439-450 (2012).

[15] Liu, D. et al. The sepallata mads-box protein slmbp21 forms protein complexes with jointless and macrocalyx as a transcription activator for development of the tomato flower abscission zone. Plant J. 77, 284-296 (2014).

[16] Szymkowiak, E. J. & Irish, E. E. JOINTLESS suppresses sympodial identity in inflorescence meristems of tomato. Planta 223, 646-658 (2006).

[17] Quinet, M., Kinet, J. M. & Lutts, S . Flowering response of the uniflora: blind:self-pruning and jointless: uniflora: self-pruning tomato (Solanum lycopersicum) triple mutants. Physiologia Plant. 141, 166-176 (2011).

[18] Schumacher, K., Schmitt, T., Rossberg, M., Schmitz, G. & Theres, K. The Lateral suppressor (Ls) gene of tomato encodes a new member of the VHIID protein family. Proc. Natl Acad. Sci. USA 96, 290-295 (1999).

[19] Mc Kim, S. M. et al. The BLADE-ON-PETIOLE genes are essential for abscission zone formation in Arabidopsis. Development 135, 1537-1546 (2008).

[20] Bürglin, T. R. Analysis of TALE superclass homeobox genes (MEIS, PBC, KNOX, Iroquois, TGIF) reveals a novel domain conserved between plants and animals. Nucleic Acids Res. 25, 4173-4180 (1997).

[21] Douglas, S. J., Chuck, G., Dengler, R. E., Pelecanda, L. & Riggs, C. D. KNAT1 and ERECTA regulate inflorescence architecture in Arabidopsis. Plant Cell 14, 547-558 (2002).

[22] Venglat, S. P. et al. The homeobox gene BREVIPEDICELLUS is a key regulator of inflorescence architecture in Arabidopsis. Proc. Natl Acad. Sci. USA 99, 4730-4735 (2002).

[23] Ragni, L., Belles-Boix, E., Gunl, M. & Pautot, V. Interaction of KNAT6 and KNAT2 with BREVIPEDICELLUS and PENNYWISE in Arabidopsis inflorescences. Plant Cell 20, 888-900 (2008).

[24] Li, Y., Pi, L., Huang, H. & Xu, L. ATH1 and KNAT2 proteins act together in regulation of plant inflorescence architecture. J. Exp. Bot. 63, 1423-1433 (2012).

[25] Byrne, M. E. Phyllotactic pattern and stem cell fate are determined by the Arabidopsis homeobox gene BELLRINGER. Development 130, 3941 (2003).

[26] Smith, H. M. & Hake, S. The interaction of two homeobox genes, BREVIPEDICELLUS and PENNYWISE, regulates internode patterning in the Arabidopsis inflorescence. Plant Cell 15, 1717-1727 (2003).

[27] Smith, H. M., Campbell, B. C. & Hake, S. Competence to respond to floral inductive signals requires the homeobox genes PENNYWISE and POUND-FOOLISH. Curr. Biol. 14, 812-817 (2004).

[28] Bhatt, A. M., Etchells, J. P., Canales, C., Lagodienko, A. & Dickinson, H. VAAMANA-a BEL1-like homeodomain protein, interacts with KNOX proteins BP and STM and regulates inflorescence stem growth in Arabidopsis. Gene 328, 103-111 (2004).

[29] Yan, F. et al. SlBL4 regulates chlorophyll accumulation, chloroplast development and cell wall metabolism in tomato fruit. J. Exp. Bot. 71, 5549-5561 (2020).

[30] Deng, W. et al. The tomato SlIAA15 is involved in trichome formation and axillary shoot development. N. Phytologist 194, 379-390 (2012).

[31] Fillatti, J. J., Kiser, J., Rose, R. & Comai, L. Efficient transfer of aglyphosate tolerance gene into tomato using a binary Agrobacterium tumefaciens vector. Nat. Biotechnol. 5, 726-730 (1987).

[32] Yan, Fang et al. Ectopic expression a tomato KNOX Gene Tkn4 affects the formation and the differentiation of meristems and vasculature. Plant Mol. Biol. 89, 589-605 (2015).

[33] Ma, C. et al. A knotted1-like homeobox protein regulates abscission in tomato by modulating the auxin pathway. Plant Physiol. 167, 844-853 (2015).

[34] Barry, C. S. et al. Altered chloroplast development and delayed fruit ripening caused by mutations in a zinc metalloprotease at the lutescent2 locus of tomato. Plant Physiol. 159, 1086-1098 (2012).

[35] Hellens, R. P. et al. Transient expression vectors for functional genomics, quantification of promoter activity and RNA silencing in plants. Plant Methods 1, 13 (2005).

[36] Sexton, R. & Roberts, J. A. Cell biology of abscission. Annu. Rev. Plant Biol. 33, 133-162 (1982).

[37] Hay, A. & Tsiantis, M. KNOX genes: versatile regulators of plant development and diversity. Development 137, 3153-3165 (2010).

[38] Lanhuan, Meng et al. 2018. BEL1-LIKE HOMEODOMAIN 11 regulates chloroplast development and chlorophyll synthesis in tomato fruit. Plant J. 94, 1126-1140 (2018).

[39] Patterson, S. E. Cutting loose Abscission and dehiscence in Arabidopsis. Plant Physiol. 126, 494-500 (2001).

[40] Mayer, K. F. et al. Role of WUSCHEL in regulating stem cell fate in the Arabidopsis shoot meristem. Cell 95, 805-815 (1998).

[41] Muller, D., Schmitz, G. & Theres, K. Blind homologous R2R3 Myb genes control the pattern of lateral meristem initiation in Arabidopsis. Plant Cell 18, 586-597 (2006).

[42] Raman, S. et al. Interplay of miR164, CUP-SHAPED COTYLEDON genes and LATERAL SUPPRESSOR controls axillary meristem formation in Arabidopsis thaliana. Plant J. 55, 65-76 (2008).

[43] Meir, S. et al. Microarray analysis of the abscission-related transcriptome in the tomato flower abscission zone in response to auxin depletion. Plant Physiol. 154, 1929-1956 (2010).

[44] Schmitz, G. et al. The tomato Blind gene encodes a MYB transcription factor that controls the formation of lateral meristems. Proc. Natl Acad. Sci. USA 99, 1064-1069 (2002).

[45] Manojit, M. B. et al. The manipulation of auxin in the abscission zone cells of Arabidopsis flowers reveals that indoleacetic acid signaling is a prerequisite for organ shedding. Plant Physiol. 162, 96-106 (2013).

[46] Shi, Z. et al. SlPIN1 regulates auxin efflux to affect flower abscission process. Sci. Rep. 7, 14919 (2017).

[47] Pattison, R. J. & Carmen, C. Evaluating auxin distribution in tomato (Solanum lycopersicum) through an analysis of the PIN and AUX/LAX gene families. Plant J. 70, 4 (2012).

[48] Swarup, K. et al. The auxin influx carrier LAX3 promotes lateral root emergence. Nat. Cell Biol. 10, 946-954 (2008).

[49] Vandenbussche, F. et al. The auxin influx carriers AUX1 and LAX3 are involved in auxin-ethylene interactions during apical hook development in Arabidopsis thaliana seedlings. Development 137, 597-606 (2010).

[50] Ellis, C. M. et al. Auxin Response Factor1 and Auxin Response Factor 2 regulate senescence and floral organ abscission in Arabidopsis thaliana. Development 132, 4563-4574 (2005).

[51] Guan, X. et al. Temporal and spatial distribution of auxin response factor genes during tomato flower abscission. J. Plant Growth Regul. 33, 317-327 (2014).

[52] Srivignesh, S. et al. (2016). De novo transcriptome sequencing and development of abscission zone-specific microarray as a new molecular tool for analysis of tomato organ abscission. Front. Plant Sci. 6, 1258 (2016).

[53] Lashbrook, C. C., Gonzalez-Bosch, C. & Bennett, A. B. Two divergent indo-b-1,4-glucanase genes exhibit overlapping expression in ripening fruit and abscising flowers. Plant Cell 6, 1485-1493 (1994).

[54] Kalaitzis, P., Solomos, T. & Tucker, M. L. Three different polygalacturonases are expressed in tomato leaf and flower abscission, each with a different temporal expression pattern. Plant Physiol. 113, 1303-1308 (1997).

[55] Lashbrook, C. C., Giovannoni, J. J., Hall, B. D., Fisher, R. L. & Bennett, A. B. Transgenic analysis of tomato endo-b-1,4-glucanase gene function: role of Cel1 in floral abscission. Plant J. 13, 303-310 (1998).

[56] Agustí, J., Merelo, P., Cercós, M., Tadeo, F. R. & Talón, M. Ethylene-induced differential gene expression during abscission of citrus leaves. J. Exp. Bot. 59, 2717-2733 (2008).

[57] Agustí, J. et al. Comparative transcriptional survey between laser-microdissected cells from laminar abscission zone and petiolar cortical tissue during ethylene-promoted abscission in citrus leaves. BMC Plant Biol. 9, 127 (2009).

[58] Roberts, J. A. & Gonzalez-Carranza, Z. H. Pectinase function in abscission. Stewart Postharvest Rev. 5, 1-4 (2009).

[59] Kim, J. Four shades of detachment: regulation of floral organ abscission. Plant Signal Behav. 9, e976154 (2014).

[60] Merelo, Paz et al. Cell wall remodeling in abscission zone cells during ethylene-promoted fruit abscission in citrus. Front. Plant Sci. 8, 126 (2017).

[61] Song, L., Valliyodan, B., Prince, S., Wan, J. & Nguyen, H. Characterization of the XTH gene family: new insight to the roles in soybean flooding tolerance. Int. J. Mol. Sci. 19, 2705 (2018).

[62] Jiang, C. Z., Lu, F., Imsabai, W., Meir, S. & Reid, M. S. Silencing polygalacturonase expression inhibits tomato petiole abscission. J. Exp. Bot. 59, 973-979 (2008).

[63] Kalaitzis, P., Koehler, S. M. & Tucker, M. L. Cloning of a tomato polygalacturonase expressed in abscission. Plant Mol. Biol. 28, 647-656 (1995).

[64] Hong, S. B., Sexton, R. & Tucker, M. L. Analysis of gene promoters for two tomato polygalacturonases expressed in abscission zones and the stigma. Plant Physiol. 123, 869-881 (2000).

[65] Brummell, D. A., Hall, B. D. & Bennett, A. B. Antisense suppression of tomato endo-1,4-beta-glucanase Cel2 mRNA accumulation increases the force required to break fruit abscission zones but does not affect fruit softening. Plant Mol. Biol. 40, 615-622 (1999).

[66] Cho, H.-T. & Cosgrove, D. J. Altered expression of expansin modulates leaf growth and pedicel abscission in Arabidopsis thaliana. Proc. Natl Acad. Sci. USA 97, 9783-9788 (2000).

[67] Lee, Y., Choi, D. & Kende, H. Expansins: ever-expanding numbers and functions. Curr. Opin. Plant Biol. 4, 527-532 (2001).

[68] Cosgrove, D. J. et al. The growing world of expansins. Plant Cell Physiol. 43, 1436-1444 (2002).

[69] Belfield, E. J., Ruperti, B., Roberts, J. A. & McQueen-Mason, S. Changes in expansion activity and gene expression during ethylene-promoted leaflet abscission in Sambucus nigra. J. Exp. Bot. 56, 817-823 (2005).

[70] Kim, J. et al. Examination of the abscission-associated transcriptomes for soybean, tomato and Arabidopsis highlights the conserved biosynthesis of an extensible extracellular matrix and boundary layer. Front. Plant Sci. 6, 1109 (2015).

[71] Tucker, M. L., Burke, A., Murphy, C. A., Thai, V. K. & Ehrenfried, M. L. Gene expression profiles for cell wall-modifying proteins associated with soybean cyst nematode infection, petiole abscission, root tips, flowers, apical buds, and leaves. J. Exp. Bot. 58, 3395-3406 (2007).