Shoot apical meristem (SAM) progresses into aninflorescence meristem (reproductive phase) when molecular/environmentalsignals are transmitted to it. Transcript abundance of majority of genesincreased from vegetative (VS) to reproductive stage I (RSI). Gene transcriptsof SUP, TFL1and AP1 was increasedup to 426 folds. Expression of CUC2, CRY2, PIN1 and TAA1 genes wasupregulated to ~5 folds at RSI as compared to vegetative phase.
This showedthat majority of genes involved in reproductive phase transition are floralhomeotic 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 activein this transition. However, genes AG,DYAD, FLO, SPA, IPT9, SBP, CTR1 and ERAF17 did not show significant changein transcripts level at RSI (Fig. II).
4.2.2Expression analysis at RSI and RSII stagesAfter transition of SAM towards reproductivephase, initial buds are formed. Thus, at this stage reproductive organs begins to form.
Genescontributing in this transition are, AP1,CUC2, RGL, EIN2 and IPT2, TypA1, PIN1. Expressionof TypA1, PIN1 and AP1 wasincreased up to 1953 folds at RSII whereas genes CUC2, RGL, IPT2 and EIN2 showed an increase in expression of ~13 folds. Other geneswhich 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 ascompared to RSI (Fig. II). Most ofthe genes with higher expression at transition to RSII were involved incytokinin, ethylene, auxin signaling and circadian rhythm pathway and arehighly active in floral organs.
CUC2,AP1, RGL and FLO are the transcriptionfactors which showed higher expression in RSII, thus, involved in signaling forfloral organ formation. Genes CTR1, ETR1, ACS7 and EIN2 are knownto play role in ethylene signaling pathway and showed their contribution infloral organ formation.4.
2.3 Expression analysis of genes atRSIII, RSIV and RSV stages Initial buds develop and differentiate into eithermale 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 stageRSV followed by ~18 folds, ~ 3 folds increase at RSIII and RSIV, respectively. SUP, a zinc finger protein showed highestexpression at RSIII with ~43 folds as compared to RSIV (~2 folds) and RSV (~29 folds). CRY2 gene showed higherexpression in RSIII (~8 folds) and RSV (~7.5 folds) as compared to RSIV (~3.5folds).
Expression of genes IPT1, IPT2, IPT3, and CKI1 showed ~2folds higher in RSV as compared to RSIV (Fig.II). Genes TAA1 and PIN1 involved in auxin biosynthesis andflux 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 betweencytokinin and auxin signaling pathways might be regulating female flowerdevelopment. Similarly, TFL1, AP1 and TypA1 might be contributing in developmentof male flowers.
TFL1 gene expressedhighest in RSIII (~81 folds) followed by RSIV (~67 folds) and RSV (~63 folds). Genes AP1and TypA1 showed highest expressionat RSIV (~1607and ~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 thethree stages RSIII, RSIV and RSV (Fig.II).