El miedo y el otro

Flowering time is often described in the context of days to flowering (DTF) and the node of flower development (NFD). This thesis determined a moderate (Chapter 3) to strong (Chapter 4 and 6) positive correlation between both DTF and NFD in lentil. Chapter 4 also determined that NFD in lentil is a complex trait, and postulates that two independent traits; node of floral initiation (NFI) and

delay to flower development (DFD) contribute to the observed variation for NFD (refer to Figure 7-1A for illustration).

7.1.1 Photoperiod-independent regulation

Findings from this thesis propose that in lentil each of the defined node-based traits for flowering are a function of individual pathways that synergistically regulate the shift to an optimal flowering phenology. In Chapter 4, a novel locus designated QTLA, is described to control DTF (Figure 4-6) and the developmental node for NFI (Figure 4-12). The chapter also determined that NFI is regulated independently of photoperiod.

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Figure 7-1 Proposed model for the genetic control of flowering time in lentil.

(A) Traits contributing to flowering time variation. Loci implicated in the control of flowering time are illustrated. NFD refers to the node of flower development,NFI refers to the node of flower initiation, DFD refers to the node interval between NFI and NFD. (B) The mode of action of loci determined in this thesis is illustrated. Arrows indicate loci promoting flowering, while bars loci inhibiting flowering. In both figures, ‘black-white’ loci indicate unknown molecular basis, the ‘sun and moon’ symbols indicate photoperiodic basis, and red ‘?’ indicate that more work is required.

Chapter 5 proposes that expressed non-coding RNA (ncRNA) form the molecular basis for QTLA (Figure 5-6), and that it acts through the regulation of FTa1 and

FTa2 (Figure 5-3 and Figure 7-1B). It is not known how this is achieved, but precedence in the mice system point to the likely epigenetic regulation of the ncRNA that facilitate the promotion and repression of neighbouring genes.

The proposed photoperiod-independent pathway, and its control of the first floral structure, draws interesting parallels to observations of a photoperiod- insensitive pre-inductive phase described by Roberts et al. (1986) for lentils. Roberts et al. (1986) had inferred that this phase is the juvenile phase or basic vegetative phase, and his findings point to a variation (time) for his phase across evaluated accessions.

The elevated expression of both FTa1 and FTa2 during early development of early flowering ILL 2601 (Figure 5-3) furthermore mirrors observations by Jaudal et al. (2013) of M. truncatula vernalisation mutants. Jaudal et al. (2013) additionally determined that retroelement insertions 3’ of FTa1 can eliminate

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vernalisation requirements and confer a dominant early-flowering phenology in

M. truncatula. This resembles the dominant flowering habit conferred by the ILL 2601 haplotype for the FTa1-FTa2 intergenic region (Figure 5-7). While this thesis does not explore vernalisation, Summerfield et al. (1985) and Roberts et al. (1986) have determined that in lentil vernalisation can reduce the nominal base photoperiod required for flower induction, and shorten the critical photoperiod required for flowering.

It is of interest to the study of flowering time in lentil to validate the role of the novel QTLA in the vernalisation response. Findings from Chapters 4 and 5 present opportunities for future work in the area.

7.1.2 Photoperiod-dependent regulation

The existing literature on the photoperiodic basis for flowering (Roberts et al., 1988; Roberts et al., 1986; Summerfield et al., 1985), and flowering time variation (Erskine et al., 1990a; Erskine et al., 1994), imply the presence of a photoperiod-dependent pathway for flowering time in lentil. Inference from previous work on the lentil Sn (Sarker et al., 1999) and cv. Precoz (Roberts et al., 1986) suggests a photoperiodic basis for the previously characterised flowering time locus. Chapter 3 determined that the lentil Sn locus is orthologous to the

ArabidopsisELF3 circadian clock gene (Figure 3-5), and that the recessive elf3-1

alleles derived from cv. Precoz afford an early flowering phenology by conferring photoperiod-insensitivity (Figure 3-4).

Chapter 4 defines two novel lentil flowering time loci, designated QTLB and

QTLC, implicated in the photoperiod-dependent pathway (Figure 4-1 and Figure 4-6). Chapter 5 proposes that the newly defined QTLB flowering time locus is a legume-specific PRR paralogue and that mutant prr59c alleles from ILL 2601 similarly afford an early flowering phenology by conferring photoperiod- insensitivity. While it can be inferred from other systems that the legume- specific PRR paralogue acts to regulate the circadian rhythm, its mode of action remains unclear.

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7.1.3 Interplay between flowering pathways

The development of the first open flower as illustrated in Figure 7-1A, begins with the initiation of a floral structure at NFI. However, findings from Chapter 4 and anecdotal observations in Chapter 3 show that this floral structure is unlikely to develop into an open flower in photoperiod-responsive plants (ILL 5588) under non-inductive short days.

A delay (DFD) characterised by repeated floral abortions is suggested to occur under non-inductive short days (Figure 7-1A). Plants with photoperiod defects (ILL 6005 and ILL 2601) do not demonstrate floral abortions under short days; instead develop an open flower at the first reproductive node. Similarly, photoperiod-responsive plants (ILL 5588 and cv. Indianhead) are observed to develop an open flower at the first reproductive node under inductive long days. The interplay between the both pathways manifests through DFD.

Observations from this thesis further point to the requirement for inductive photoperiod for flowering, consistent with findings by Roberts et al. (1986) and Summerfield et al. (1985) that determined that while the critical base photoperiod can be reduced, presumably by QTLA, the requirement for photoperiod cannot be eliminated. The photoperiod-dependent basis for DFD also mirrors findings by Jaudal et al. (2013), that in plants with retroelement insertions 3’ of FTa1, there still is a requirement for inductive photoperiod.

It is not known how these pathways interact or synergistically act to regulate flowering time. Chapter 5 introduces the role of Arabidopsis FT orthologues in lentil flowering time regulation. It had been reviewed by Weller et al. (2015) that in P. sativum and G. max, these floral promoters act as floral integrators. It is suggested that both photoperiod (Hecht et al., 2011) and vernalisation (Laurie et al., 2011) are involved in the regulation of legume-specific FTs. Findings from Chapter 5 suggest that QTLA acts on FTa1 and FTa2. FTc however is likely to be further downstream of the flowering pathway, as its expression mirrors the appearance of flower buds in lentil.

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Separately, Chapter 6 of this thesis introduces two new loci involved in conferring a late-flowering phenology under inductive long day photoperiods. It is unclear from findings in this thesis how these loci interact or act in relation to the defined loci and described flowering pathways.