Regulation of vegetative and generative reproduction in the woodland strawberry

Unlike annual plants, perennials have repeated cycling between the vegetative and generative stages. Studying the balance between these two phases would enable breeders to produce higher quality crops. The woodland strawberry is used as a model to study developmental patterns in perennials because it has a wide geographical distribution, a small sequenced genome, and a number of available natural mutants, which provide excellent resources for physiological, molecular and genetic studies. This thesis investigated the genetic and environmental coordination of shoot apical meristem (SAM) and axillary meristem (AXM) fates in woodland strawberry. In woodland strawberry, SAM forms an inflorescence after flower induction, whereas AXMs can differentiate either into runners or branch crowns that are able to form additional inflorescences. Genetic mapping and the experiments using transgenic lines and natural accessions with contrasting environmental responses showed that a number of genes regulated the balance between vegetative and generative development in woodland strawberry. In general, cool temperature or short days (SD) induced flowering and promoted AXM differentiation to branch crowns, while warm temperature and long days (LD) promoted runner formation. High levels of FvTERMINAL FLOWER1 (FvTFL1) expression in FvTFL1 overexpression lines and NOR1 accession inhibited flowering at temperatures of 10-22°C in both SD and LD, but the environmental control of AXM fate was not affected in these plants indicating that environment influenced AXM differentiation irrespective of flowering. In the seasonal flowering genotype, FvSUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (FvSOC1) was observed to quantitatively increase runner formation. The photoperiodic control of flowering and AXM fate was studied in more detail using FvCONSTANS (FvCO) and FvFLOWERING LOCUS T1 (FvFT1) transgenic lines. These studies showed that FvCO controls the expression of FvFT1, and they both have a major role in the control of the balance between the vegetative and generative development in SD and LD. Genetic mapping studies under differing environments identified five QTLs that, together, explained about half of the observed flowering time variance in the mapping population, and two additional QTLs were identified for the number of branch crowns explaining about 20% of variance. The flowering time QTL on LG6 colocalized with FvTFL1, and one of the QTL regions on LG4 that controlled both flowering time and AXM fate was close to the PFRU, a previously identified locus in the commercial strawberry. Among the previously unknown loci, two flowering time QTLs on LG7 colocalized with putative flowering time genes FvEARLY FLOWERING 6 (FvELF6) and FvCENTRORADIALIS1 (FvCEN1), a homolog of FvTFL1. Furthermore, a gene encoding TCP transcription factor and a homolog of DORMANCY ASSOCIATED MADS BOX (DAM) were identified as candidate genes in QTL regions controlling AXM fate on LG4 and LG5, respectively. This study shed new light into the genetic and environmental control of AXM and SAM fates providing new means to control the balance between vegetative and generative reproduction under different environmental conditions.