**7. Conclusion and future prospects**

Sequence analysis showed that OsKAN1 consists of six exons. Phylogenetic and comparative genetic analysis indicated that OsKAN1 is an ortholog of AtKANs and is most closely related to AtKAN4. The predicted OsKAN1 polypeptide contains a potential phosphorylation site in the C-terminal region which may be important for interaction with other proteins involved in signaling. The overall identity between *KANADI* family members is low, but they are nearly identical within the GARP domain. The sequence similarity found in this subset of GARP genes may indicate that they have overlapping or partially redundant

Suppression of OsKANADI1 by RNAi displayed branching and increasing tiller number in several lines [44]. This phenotype resembles to the Hd3a overexpressed plants indicating that they possibly function in similar pathway. Further characterization using the OsKANADI

The role of Hd3a as flowering mobile signal in rice and *Arabidopsis* leads to investigation of its function in another plants. The diverse role of FT was identified in many plants. FT protein involved in vernalization, stomatal opening, dormancy and tuberization [45–48]. Navarro et al. [49] provided a new insight in understanding the florigen as graft-transmissible signal and designated its role as tuberi. Hd3a homolog were overexpressed in potato under noninductive long-day condition and resulting in tuberization and flower development. A grafting experiment using tobacco florigen as scion and potato as rootstock to test the hypothesis confirmed that FT proteins were transmitted from scion to rootstock and induced tuberization.

The flowering and tuberization pathway are regulated in different pathways, indicating that FT has many homolog in potato. This hypothesis was confirmed by Navarro et al. [49]. In potato, there are three homolog of FT. StSP3A regulate the tuber formation, StSP3D regulate the flowering, and StSP5G as the repressor of tuberization. Expression of *StSP6A* gene is strong in leaves and stolon of short-day induced plants. Interestingly, 30-minute night break was reported to inhibit tuberization. The *StSP3D* expression is necessary for flowering induction. However, this gene is not required for normal tuberization. Interestingly, the StSP5G is an antagonist for StSP6A. The expression of StSP5G was high in long-day condition [47]. The role of Hd3a/FT protein in potato flowering and tuberization is well understood. This photo-

Recent study in onion tuberization reveals that its induction is controlled by Hd3a/FT homolog in the photoperiodic pathway. Onion is a biennial plant that forms tuber during the summer and flower after the winter in the next summer. There are many Hd3a/FT homologs found in onion and the pattern is the same with potato. There are Hd3a/FT homologs that regulate the tuber/bulb formation (AcFT1 and AcFT4) and flowering (AcFT2) [50]. As seen in potato tuberization, AcFT4 in onion has the same role as StSP5G in potato that inhibits onion tuber formation; while AcFT1 is a strong inducer for tuberization (tuberigen) under long-day condition. This finding suggests that Hd3a/FT has a versatile role in plant development.

mutants plants in the next generation remains to be investigated.

This experiment suggests that FT/Hd3a is a strong tuberization inducer.

periodic pathway is conserved in potato, rice, and *Arabidopsis*.

**6. Hd3a homolog in plant development**

functions.

62 Plant Engineering

As the floral stimulus that controls floral transition in the SAM, Hd3a has the capacity to traffic from cell to cell and move long distances via the phloem. To reveal its function, Hd3a recruits different proteins in plant developmental stage. A wide range of proteins that interact with Hd3a were identified using yeast two-hybrid screening. GF14c (a 14-3-3 homolog), OsKANADI (a novel transcription factor containing a GARP domain), and the BRI1 kinase domain-interacting protein 116b (BIP116b) are the Hd3a interactors of interest. It is possible that Hd3a and its partner(s) may form a platform for cross-talk between signal transduction pathways. Another homolog of Hd3a in many plants was identified and it was suggested that Hd3a/FT has versatile role in plant development. This role depends on its partner and interaction to gain its function. Further study using reverse genetics to obtain mutants, either gain-of-function mutants or suppression mutants by RNA interference of Hd3a partners to get insight into the function in plant growth and development, particularly during floral transition is important. Our understanding in floral transition in rice would make for better crop management in future and represent an important addition to our knowledge about FT signaling in plants.
