Universität zu Köln

Busch, Bernhard L. (2011). Genetic and molecular analysis of aerial plant architecture in tomato. PhD thesis, Universität zu Köln.

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Abstract

Aerial architecture of seed plants is determined by the development of repeating modules named phytomers. An important factor therein is the formation and fate of axillary meristems (AMs), influencing agronomically important traits, like inflorescence architecture and shoot branching. The present study in tomato represents a reverse genetics approach unveiling the function of genes homologous to the MYB and bHLH proteins, Blind and LAX, two key regulators of axillary meristem initiation. Public databases and PCR technology enabled the identification of three closely related paralogs of Blind, Blind-like1 (Bli1), Bli2 and Bli3. TILLING of Bli2 led to the identification of the classical tomato mutant potato leaf (c), a mutant described already more than a hundred years ago. potato leaf mutants display leaves with reduced leaflet formation and lack leaf lobing and serration. Nine potato leaf alleles were identified, all carrying a mutation in the Bli2 gene. RNA in-situ hybridisation revealed a distinct expression pattern in leaf primordia prior to leaflet formation, at positions axillary of outgrowing leaflets and marking the sinuses of leaf lobes. Ectopic expression of Blind (Bl) partially complemented the defects of c, indicating a conserved function of the two proteins. Silencing of Bli3 revealed that this gene probably acts in the same process as C, because RNAi plants displayed reduced leaf complexity. The protein similarity of Bl and C, the partial complementation of c by Bl and the phenotype of Bli3 RNAi plants represent further elements in the rising evidence that leaf dissection and AM initiation employ homologous mechanisms. Furthermore, silencing of Bli1 and Bli3 unveiled that these genes redundantly regulate AM initiation in vegetative and reproductive development. The defect in AM initiation along the shoot axis was complementary to the defect of blind mutants. RNA in-situ hybridisation showed major expression domains of Blind in the shoot apical meristem, at positions of presumptive leaf primordium formation and adaxially of leaf primordia. Additionally, Blind mRNA accumulated adaxially of new reproductive and vegetative meristems. Besides AM initiation, Bl, Bli1 and Bli3 act in the prevention of concaulescent fusions of vegetative and reproductive side-shoots. Moreover, a series of observations disclosed that Bl, Bli1 and Bli3 control the maintenance and reproductive identity of apical and axillary meristems. In a second project, silencing of the bHLH transcription factor SlLax in tomato, led to the identification of the classical mutant, uniflora. SlLax/Uniflora encodes an ortholog of the AM initiation regulators, LAX (rice), ba1 (maize) and ROB (Arabidopsis). Uniflora (Uf) was known to control inflorescence architecture and flowering time in a condition dependent manner. Detailed analysis of organogenesis in different uniflora mutant lines, unveiled that Uf controls the initiation of reproductive axillary meristems and regulates reproductive meristem identity. RNA in-situ hybridisation indicated that Uf mRNA accumulates adaxially of newly initiated reproductive AMs, similar to the expression pattern of Blind in inflorescences. Heterodimers of bHLH and MYB proteins regulate several developmental processes. Previous studies showed that the Uf and Blind orthologous proteins ROB and RAX of Arabidopsis interact physically. The phenotypic similarities of Uf and Bl, Bli1 and Bli3 loss of function plants, and the overlapping expression patterns of Uf and Bl strongly suggest that also in tomato these MYB and bHLH proteins may act as heterodimers controlling AM initiation and meristem identity in reproductive development. Together, the observations in tomato, rice, maize and Arabidopsis propose that heterodimers of Blind and LAX orthologous MYB and bHLH proteins constitute a fundamental mechanism, controlling axillary meristem formation in flowering plants. In summary, the present study unveiled the identity of two classical mutants and demonstrated that genes of the Blind family and Uniflora regulate four important features of aerial plant architecture in tomato: leaf compoundness, organ separation, axillary meristem initiation and the development of apical meristems.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Busch, Bernhard L. bernd.busch@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-42139
Date:	25 May 2011
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Außeruniversitäre Forschungseinrichtungen > MPI for Plant Breeding Research
Subjects:	Natural sciences and mathematics Life sciences
Uncontrolled Keywords:	Keywords Language Potato leaf mutant, Uniflora, Blind, aerial plant architecture, tomato, leaf compoundness, axillary meristem initiation, organ separation, development of apical meristems, phytomer, plant metamer English
Date of oral exam:	22 June 2009
Referee:	Name Academic Title Theres, Klaus Prof. Dr. Wolfgang, Werr Prof. Dr.
Funders:	Max Planck Society
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/4213