New Insights into Roles of Cell Wall Invertase in Early Seed Development Revealed by Comprehensive Spatial and Temporal Expression Patterns of GhCWIN1 in Cotton    

Abstract

Despite substantial evidence on the essential roles of cell wall invertase (CWIN) in seed filling, it remains largely unknown how CWIN exerts its regulation early in seed development, a critical stage that sets yield potential. To fill this knowledge gap, we systematically examined the spatial and temporal expression patterns of a major CWIN gene, GhCWIN1, in cotton (Gossypium hirsutum) seeds from prefertilization to prestorage phase. GhCWIN1 messenger RNA was abundant at the innermost seed coat cell layer at 5 d after anthesis but became undetectable at 10 d after anthesis, at the onset of its differentiation into transfer cells characterized by wall ingrowths, suggesting that CWIN may negatively regulate transfer cell differentiation. Within the filial tissues, GhCWIN1 transcript was detected in endosperm cells undergoing nuclear division but not in those cells at the cellularization stage, with similar results observed in Arabidopsis (Arabidopsis thaliana) endosperm for CWIN, AtCWIN4. These findings indicate a function of CWIN in nuclear division but not cell wall biosynthesis in endosperm, contrasting to the role proposed for sucrose synthase (Sus). Further analyses revealed a preferential expression pattern of GhCWIN1 and AtCWIN4 in the provascular region of the torpedo embryos in cotton and Arabidopsis seed, respectively, indicating a role of CWIN in vascular initiation. Together, these novel findings provide insights into the roles of CWIN in regulating early seed development spatially and temporally. By comparing with previous studies on Sus expression and in conjunction with the expression of other related genes, we propose models of CWIN-and Sus-mediated regulation of early seed development.

Critical Roles of Vacuolar Invertase in Floral Organ Development and Male and Female Fertilities Are Revealed through Characterization of GhVIN1-RNAi Cotton Plants

“…In cotton seed, Suc is unloaded symplasmically from the phloem in the outer seed coat (Ruan et al, 1997;Wang and Ruan, 2012). High VIN activities and gene expression have been observed in wild-type cotton outer seed coat during early seed development (Wang et al, 2010), along with strong Sus expression and activity in the seed epidermis (Ruan et al, 2003).…”

“…For subsequent translocation into the filial tissues in cotton seed, assimilates must pass two symplasmically disconnected cellular sites: between the outer and inner seed coat, and between maternal and filial tissues (Ruan et al, 1997;Wang and Ruan, 2012). High CWIN expression at both interfaces may facilitate the hexose production in these sites.…”

“…Once seed coat cell expansion has initiated, it develops independently from endosperm and embryo (Haughn and Chaudhury, 2005). Thus, the seed coat in undeveloped seeds probably has received no or impaired initial signal for its growth, while the underdeveloped seeds may have acquired such a signal from the endosperm during nuclear division (approximately 3-5 DAA in cotton; Wang and Ruan, 2012), allowing their seed coats to be fully developed. Consistently, the endosperm in the underdeveloped seed appeared to develop until the cellularization stages at approximately 10 DAA ( Fig.…”

Cell wall invertase as a regulator in determining sequential development of endosperm and embryo through glucose signaling early in seed development

“…7 By using in situ hybridization, GhCWIN1 transcripts were found to be most abundant near the chalazal end of embryo sac where the syncytial (coenocytic) endosperm undergoes nuclear division, but became almost undetectable at the micropylar end where the fertilized egg sits. Taken the sucrose hydrolytic activity of invertase and the coenocytic nature of the endosperm into account, the asymmetric distribution of GhCWIN1 implies a spatial gradient of hexose within the embryo sac favoring rapid endosperm nuclear division.…”

“…6 However, little is known about the potential roles of sugar and related genes in early seed development. Here, based on recent studies on cellular domain-and stage-specific expression of cell wall invertase (CWIN) in cotton and, to a less extent, Arabidopsis, during seed development from pre-fertilization to pre-storage phases, 7 we propose that CWIN acts as an activator to positively regulate endosperm nuclear division, but not embryo development, soon after fertilization, hence shedding a light into the basis of sequential development of the two filial tissues. the coenocytic endosperm and followed by the globular embryo in early seed stages, 7 strongly suggest that CWINmediated glucose signaling plays a major role in mitotic division during early seed development.…”