**5. Transcriptional regulation of seed development for improved yield**

In the context of seed development, genotype-specific and stage-dependent temporal shifts in gene expression profile have been reported in the aleurone, embryo and endosperm, and other cell-type of maturing seeds, potentially leading to seed phenotypic differences [103, 104]. Transcriptomic studies in several plant systems has led to the identification of transcriptional programs and regulatory networks underlying molecular functions associated with cellular activities *Molecular and Transcriptional Regulation of Seed Development in Cereals: Present Status… DOI: http://dx.doi.org/10.5772/intechopen.99318*

in endosperm [105, 106], starch metabolism [107], seed storage substances and high molecular weight glutenin genes [108–110], grain quality (glycemic index) [111], post-transcriptional regulations occurs at the end of seed development [17] and programming of seed developmental and maturation processes, and elucidation of the underlying functional transitions (**Table 3**) [103].


#### **Table 3.**

*Transcriptional approaches for improved seed yield in cereal crops.*

In rice, Nie et al. [15], identified 12 classes of endosperm-specific genes, including transcription factor, stress/defense, seed storage protein (SSP), carbohydrate and energy metabolism, seed maturation, protein metabolism, lipid metabolism, transport, cell wall related, hormone related, signal transduction, and one unclassified category. In addition, several cis-regulator elements were found in the promoter region of endosperm-specific expressed genes including, AACA box, ACGT box, GCN4 motif (TGA (G/C) TCA), the prolamin box (P box: AAAG), SKN-1 *cis-*element, RY repeat (CATGCATG) [29], ABA responsive element (ABRE) motif, and transfer cell-specific motif TATCTCTATCT (C/A) from aleurone cell [126]. These elements may play an important role in regulating the temporal and spatial expression genes in endosperm development.

Based on the cis-element, the corresponding transcription factor were also determined. For example, the MYB protein specifically binds to the AACA box, and the GNC4 motif is bounded by transcription factors of the Opaque2-like basic leucine zipper (bZIP) activators (rice RISBZ1), ABRE motif by bZIP transcription factors, the P box by plant-specific DNA binding with one finger (DOF) zinc-finger transcription factors (rice RPBF), and FUSCA3 (FUS3) recognizes the RY repeats [29, 127, 128]. In addition, synergy between RPBF and RISBZ1 has been implicated in mediating the regulatory networks essential for seed development by binding to the GCN4 motif to trans-activate the expression of seed storage proteins in rice [29, 129]. Recently, Grimberg et al. [130] identified an oat endosperm homolog of WRINKLED1 transcription factor (*AsWRI1*), which when expressed under the control of endosperm-specific HMW1Dx5 promoter, causes substantial alterations in carbon allocation in wheat grains, including lower seed weight and a wrinkled seed phenotype.

Polyamines such as putresceine, Spermidine (Spd), and Spermine (Spm) have been implicated in regulation of spikelets postanthesis development [131]. Exogenous Spd and Spm are applied to rice panicles to improve grain filling and grain weight in inferior spikelets [132]. Furthermore, the concentrations of Spd and Spm are related to rice grain size. The *OsSPMS1* gene is involved in the conversion of Spd to Spm, as well as the production of 1-aminocyclopropane-1-carboxylic acid (ACC) and ethylene. Manipulation of the *OsSPMS1* gene has a significant impact on a variety of traits, including plant height, grain size, seed germination, and yield production [133]. More importantly, knockout of *OsSPMS1* increases grain production in a high-yield variety, implying that *OsSPMS1* is a key target gene for rice yield improvement [114].

During plant reproductive growth, cell-to-cell communication via receptor-like kinases (RLKs) regulates a wide range of biological processes. FLORALORGANNUMBER1 (FON1), a potential ortholog of CLAVATA1 (CLV1), interacts with the putative ligand FON2/FON4, a CLV3-related protein, to maintain the inflorescence meristem [134]. The orthologous *Catharanthus roseus* RLK1-like (CrRLK1L) subfamily has a putative carbohydrate binding malectin-like domain and is involved in a variety of biological processes [135], including male–female interactions mediated by the synergid-expressed genes FERONIA (FER), DWARF AND RUNTISH SPIKELET1 (DRUS1), and DRUS2. These two proteins, which operate as essential regulators, control reproductive growth in rice in a redundant manner by suppressing cell death and influencing sugar use [24]. Evidence has been presented in my laboratory which demonstrates that endogenous repression of *CCA1* gene under the control of *TOC1* promoter resulted in improved morphological traits: increased number of tillers/panicle, thousand seed weight, seed size; whereas, over-expression leads to diminution in morphological traits: decreased number of tillers/panicle, thousand seed weight, seed size as compared to the wild

*Molecular and Transcriptional Regulation of Seed Development in Cereals: Present Status… DOI: http://dx.doi.org/10.5772/intechopen.99318*

type in *Agrobacterium*-mediated genetically transformed T1 and T2 transgenic progeny plants of rice variety Taipei 309 [136].
