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Shoot apical meristem (SAM) progresses into an
inflorescence meristem (reproductive phase) when molecular/environmental
signals are transmitted to it. Transcript abundance of majority of genes
increased from vegetative (VS) to reproductive stage I (RSI). Gene transcripts
of SUP, TFL1and AP1 was increased
up to 426 folds. Expression of CUC2, CRY2, PIN1 and TAA1 genes was
upregulated to ~5 folds at RSI as compared to vegetative phase. This showed
that majority of genes involved in reproductive phase transition are floral
homeotic genes and belong to different classes of transcription factors. TAA1 (encoding L-tryptophan-pyruvate aminotransferase) and PIN1 genes associated with auxin biosynthesis and flux were also active
in this transition. However, genes AG,
DYAD, FLO, SPA, IPT9, SBP, CTR1 and ERAF17 did not show significant change
in transcripts level at RSI (Fig. II).

4.2.2
Expression analysis at RSI and RSII stages

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After transition of SAM towards reproductive
phase, initial buds are formed. Thus, at this stage reproductive organs begins to form. Genes
contributing in this transition are, AP1,
CUC2, RGL, EIN2 and IPT2, TypA1, PIN1. Expression
of TypA1, PIN1 and AP1 was
increased up to 1953 folds at RSII whereas genes CUC2, RGL, IPT2 and EIN2 showed an increase in expression of ~13 folds. Other genes
which might be responsible for bud formation are CEN1, BEL1, CRY1, CYP735A, TAA1, WUS, STY, FLO, FT, REV, AHK2, CRE1, CKX1, CTR1 and ACS1. They showed upto 8 folds higher expression in RSII as
compared to RSI (Fig. II). Most of
the genes with higher expression at transition to RSII were involved in
cytokinin, ethylene, auxin signaling and circadian rhythm pathway and are
highly active in floral organs. CUC2,
AP1, RGL and FLO are the transcription
factors which showed higher expression in RSII, thus, involved in signaling for
floral organ formation. Genes CTR1, ETR1, ACS7 and EIN2 are known
to play role in ethylene signaling pathway and showed their contribution in
floral organ formation.

4.2.3 Expression analysis of genes at
RSIII, RSIV and RSV stages       

Initial buds develop and differentiate into either
male or female or intermediate flowers. Genes CRY2, TAA1, CUC2, PIN1, FT, CKX1, and SUP possibly contribute towards female flower formation. SUP and CRY2 genes showed ~59 folds increase in transcript level in stage
RSV followed by ~18 folds, ~ 3 folds increase at RSIII and RSIV, respectively. SUP, a zinc finger protein showed highest
expression at RSIII with ~43 folds as compared to RSIV (~2 folds) and RSV (~29 folds). CRY2 gene showed higher
expression in RSIII (~8 folds) and RSV (~7.5 folds) as compared to RSIV (~3.5
folds). Expression of genes IPT1, IPT2, IPT3, and CKI1 showed ~2
folds higher in RSV as compared to RSIV (Fig.
II). Genes TAA1 and PIN1 involved in auxin biosynthesis and
flux are more active in RSV. Genes IPT1,
IPT2, IPT3, IPT9, CKX1, CKI1, AHK2, CRE1, CUC2, TAA1 and PIN1 followed expression pattern in the order as RSV
> RSIII >RSIV. These expression patterns indicated that interplay between
cytokinin and auxin signaling pathways might be regulating female flower
development.

Similarly, TFL1, AP1 and TypA1 might be contributing in development
of male flowers. TFL1 gene expressed
highest in RSIII (~81 folds) followed by RSIV (~67 folds) and RSV (~63 folds).  Genes AP1
and TypA1 showed highest expression
at RSIV (~1607
and ~8 folds) followed by RSIII (~1520 and ~6 folds) and RSV (~709 and ~2 folds), respectively. Genes CLV1, FLO, CYP735A, AG, DAD1, IPT9, ETR1, ACS7 and CTR1 did not show significant change in expression level in all the
three stages RSIII, RSIV and RSV (Fig.
II).

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