Our research program is focused on elucidating key questions related to auxin synthesis, translocation and the nature of auxin-regulated signaling networks during fruit development, using tomato as a model system.
During fruit set, the growth of an otherwise static ovary is stimulated after successful pollination and fertilization. After fertilization, tomato fruit growth is due primarily to cell division and later fruit growth continues mostly by cell expansion. At the end of the cell expansion period, the fruit has reached its final size and will start to ripen.
Auxin homeostasis during tomato fruit growth and development
Despite major advances made in recent years in many aspects of auxin metabolism, transport and signaling in vegetative tissues, the information about the nature and importance of these processes in fruit development and ripening of crop fruit species is very scarce. Moreover a recurring theme that emerges from all these studies is the lack of knowledge about the sources of auxin in fruit tissues, its biosynthetic pathway(s) and how auxin becomes distributed to fruit target tissues. Our research goal is to better understand the mechanisms by which auxin is produced and transported in tomato fruit and how these mechanisms are regulated to mediate cell and tissue specific growth and differentiation.
Expression of the DR5rev::mRFP auxin-responsive promoter in tomato ovaries and fruit. DR5 is a widely used auxin-responsive promoter and red fluorescence protein (RFP) signal therefore indirectly reflects auxin concentration. The top images correspond to flower buds six days before fertilization and show RFP fluorescence in the ovules confined to the micropylar pole of the embryo sac. Lower images correspond to six-day old fruit showing strong localized fluorescence in the seed funiculus.
Analysis of auxin levels or activity in different tomato tissues have revealed a dynamic pattern of tissue specific auxin accumulation throughout fruit development likely to be regulated by components of the auxin polar transport pathway. Critical components of auxin transport systems are the PIN and AUX/LAX protein families, which control cellular auxin efflux and influx respectively. Our studies have provided a transcriptional map for the PIN and AUX/LAX gene families of auxin transport facilitators in the tomato fruit, an important first step towards unraveling the complex network controlling auxin transport routes during fruit set and growth. Multiple PIN and AUX/LAX genes show both overlapping, and tissue-specific patterns of expression suggesting that the coordinated action of PIN and AUX proteins is required for establishing the adequate auxin pools and gradients controlling growth and differentiation in fruit tissues. We also seek to elucidate the mechanisms of IAA biosynthesis in tomato fruit and we are focusing on the tomato orthologs of the tryptophan aminotransferase of Arabidopsis (TAA1) which converts tryptophan into the IAA precursor indole-pyruvic acid and is a key enzyme contributing to IAA production in vivo.
The hypothesis underlying our research is that a tightly regulated spatial and temporal control of auxin levels during tomato fruit development is necessary to activate ovary growth upon fertilization and to coordinate cell expansion and differentiation during exponential fruit growth. We are testing this hypothesis by manipulating the gene expression of specific auxin transporters and auxin biosynthetic genes using fruit-specific promoters and analyzing the effect on fruit development and the dynamics of auxin distribution.
Cell-specific analysis of the tomato fruit transcriptome for the discovery of genes and networks regulating fruit development
One of the first objectives of this research, funded by the NSF Plant Genome Program, is to generate a comprehensive assessment of the cell specific transcript landscape of the developing tomato fruit using Laser Capture Microdissection (LCM) coupled with mRNA profiling by the Illumina platform.
We are mining the tissue-specific transcript datasets for genes associated with hormone signaling, synthesis and transport and with cell wall biosynthesis and modification processes. This non-targeted approach has the potential to dramatically increase the discovery of rare and cell-type specific transcripts and will help identify regulatory hormonal networks controlling auxin homeostasis, as well as new/novel components in the auxin biosynthetic, transport and response pathways. We are using this information to build a model integrating hormone regulated cell expansion and tissue growth and to identify pathways potentially critical to fruit set and growth.
Catala, C., Howe, K.J., Hucko, S., Rose, J.K.C. and Thannhauser, T.W. 2011. Towards characterization of the glycoproteome of tomato (Solanum lycopersicum) fruit using Concanavalin A lectin affinity chromatography and LC-MALDI-MS/MS analysis. Proteomics 11: 1530-1544
Pattison, R. J., Catala, C. 2011. Evaluating auxin distribution in tomato (Solanum lycopersicum) through an analysis of the PIN and AUX/LAX gene families. The Plant Journal 0: DOI:10.1111/j.1365-313X.2011.04895.x
Urbanowicz, B.R., Catala. 2007. A Tomato Endo-Β-1,4-glucanase, SlCel9C1, Represents a Distinct Subclass with a New Family of Carbohydrate Binding Modules (CBM49). J. Biol. Chem 282: 12066-12074
Isaacson, T., Damasceno, C.M.B., Saravanan, R.S., He, Y., Catala. 2006. Sample extraction techniques for enhanced proteomic analysis of plant tissues.. Nature Protocols 1: 769 -774
Saladi, Rose, J.K.C., Cosgrove, D.J. and Catala. 2006. Characterization of a new xyloglucan endotransglucosylase/hydrolase (XTH) from ripening tomato fruit and implications for the diverse modes of enzymic action. Plant J 47: 282-295
Rose J.K.C., Saladi. 2004. The plot thickens: new perspectives of primary cell wall modification. Current Opinion in Plant Biology 7: 296-301
Rose J.K.C., Catala. 2003. Plant cell wall disassembly. In The Plant Cell Wall. Annual Plant Reviews Series. Ed. J.K.C. Rose, Pub. Blackwell Publishing pp 0: 264-324
Catala, Rose, J.K.C., York, W.S, Albersheim, P, Darvill, A.G. and Bennett, A.B. 2001. Characterization of a tomato xyloglucan endotransglycosylase gene that is down-regulated by auxin in etiolated hypocotyls. Plant Physiol 127: 1180-1192
Catala, Rose, J.K.C. and Bennett, A.B. 2000. Auxin-regulated genes encoding cell wall modifying proteins are expressed during early tomato fruit growth. Plant Physiol 122: 527-534
Catala, . 1998. Cloning and sequence analysis of TomCel8; a new plant endo-1,4-Β-d-glucanase gene, encoding a protein with a putative carbohydrate binding domain (Accession No. AF098292). Plant Physiol 118: 1535
Catala, Rose, J.K.C. and Bennett, A.B. 1997. Auxin-induction and spatial localization of a novel endo-1,4-Β-d-glucanase and a xyloglucan endotransglycosylase in tomato hypocotyls. Plant J 12: 417-426
How do plant hormones control fruit development?
feature released -2008
When home gardeners or horticulturalists grow plants from stem cuttings, they often dip the cut end of the stem in a white powder that encourages the stem to develop roots. The white powder is a hormone, called an auxin, which plays an important role in plant growth and development. Auxins also influence cell division and differentiation, which is why the powder form used by gardeners helps the stem cutting to start growing root cells.
Itâ€™s also known that auxins, particularly one called indole- 3-acetic acid, are central to the development and ripening of fruit, such as strawberries and tomatoes. But very little is known about the molecular basis of auxin production, transport and signalling in fleshy fruit-producing plants. This is the area of research that Carmen Catala is pursuing at BTI.
Until now, the majority of research into auxins has been done in the model plant Arabidopsis, which is a flowering plant that only produces a dry fruit. Work on auxins has been conducted with strawberries, however, and has proven that the hormone is produced in the tiny seeds that speckle the outside of the berry, and that this auxin helps the fruit grow. It also has been found that when the berry is ready to ripen, the auxin is inactivated. A molecular explanation of how and why this happens in strawberries remains elusive.
Catala is applying knowledge gained about auxins in Arabidopsis and strawberries and using new molecular techniques to understand exactly how the auxin indole-3- acetic acid works in tomatoes. She aims to discover how and where this auxin is produced in the plant, how it is transported to the cells that will become fruit, and how it signals the cells in that tissue to grow, develop and ripen. What Catala learns in tomatoes will be applicable to other fleshy fruits as well, including strawberries.
Knowing at the molecular level how auxins help set fruit on plants and how they influence fruit development and ripening could one day lead to higher quality fruits. And, because auxins directly stimulate or inhibit the expression of specific genes, understanding how to control the production or transport of these hormones could lead to fruits with improved flavor, texture or other unique qualities.