Aberrant seed development in Litchi chinensis is associated with the impaired expression of cell wall invertase genes

Abstract

Cell wall invertase (CWIN) are known to play important roles in seed development. However, most reports to date have focused on a single gene family member, and have mainly investigated CWIN functions during the filling stage of seed development. In this study, we found significant lower levels of CWIN protein and activity associated with seed abortion in the Litchi chinensis cultivar “Nuomici.” We identified five litchi CWIN genes and observed that the expression of LcCWIN5 was limited to the flower tissues and decreased sharply with fruit development. Silencing of LcCWIN5 expression before 28 DAA (cell division stage) resulted in perturbed liquid endosperm development, smaller seeds, and higher seed abortion rate, while silencing after 28 DAA (filling stage) had no effect on seed development. In contrast, LcCWIN2 was mostly expressed in the funicle and seed coat, and increased with fruit development. Decreased LcCWIN2 expression and CWIN activity during early seed filling coincided with smaller seeds in the cultivar “Feizixiao.” Silencing of LcCWIN2 caused a reduction in the seed size without inducing seed abortion. We propose that CWIN activity in seed maternal tissues during cell division stage is likely due to LcCWIN5 expression, which regulates early seed development. On the other hand, CWIN activity during the filling stage is due to the expression of LcCWIN2, which may promote carbon import by creating a sucrose gradient. Comparable LcCWIN5 expression, but much lower CWIN activity, detected in the funicle of “Nuomici” is consistent with post-translational regulation.

Genome-wide identification and expression analysis of SWEET gene family in Litchi chinensis reveal the involvement of LcSWEET2a/3b in early seed development

“…Fruit with a small seed is an economically desirable trait of litchi fruits, and seed size has been found to be associated with the expression levels of LcCWINs , which might affect seed development through sugar import and/or sugar signaling [45]. According to our previous study [45], 28 days after anthesis (DAA) represents a transition point between the cell division stage and the filling stage during litchi seed development. As the seed size has been determined at the cell division stage.…”

“…There was no vascular tissue in the aril and the cotyledon, indicating an apoplasmic post-phloem sucrose transport from the funicle [44]. Extremely low activities of cell wall invertase (CWIN) were detected in the seed pedicel and seed coat of fruits with small seeds [45]. Silencing of LcCWIN5 or LcCWIN2 caused a reduction in the seed size [45].…”

“…Extremely low activities of cell wall invertase (CWIN) were detected in the seed pedicel and seed coat of fruits with small seeds [45]. Silencing of LcCWIN5 or LcCWIN2 caused a reduction in the seed size [45]. It is common that CWIN and SWEETs co-expressed in the apoplasmic unloading region [46].…”

Cell Wall Invertase 3 Affects Cassava Productivity via Regulating Sugar Allocation From Source to Sink

“…Enhanced CWINV activity was detected during ovary-to-fruit transition in tomato and its LIN5 was localized to cell walls of sieve elements to facilitate phloem unloading and to generate a glucose signal for fruit set (Palmer et al, 2015). A recent study also proposed different roles of CWINV genes in seed development (Zhang et al, 2018). Therefore, this study reveals the important function of MeCWINV3 in maintaining cassava sugar homeostasis in source organs.…”

Functional Characterization of Invertase Inhibitors PtC/VIF1 and 2 Revealed Their Involvements in the Defense Response to Fungal Pathogen in Populus trichocarpa

“…By contrast, apoplastic CWI splits sucrose into hexose components that were further translocated either into intracellular compartments for the transcriptional regulation, sugar metabolism, and polysaccharide biosynthesis or into extracellular space for the enhancement of sink capacity and stress responses (Bihmidine et al, 2013;Proels and Hückelhoven, 2014). The promotions of CWI on seed filling and fruit set have been well attempted in a wide range of plant species like maize, rice, tomato, cotton, and litchi (Chourey et al, 2006;Wang et al, 2008;Zanor et al, 2009;Wang and Ruan, 2012;Li et al, 2013;Zhang et al, 2018), indicating that CWIs facilitate the improvement of sink cell differentiation via multiple regulatory mechanisms of sugar metabolism and signaling. Recently, overexpressing CWIs in tobacco and tomato resulted in the deferral of leaf aging and drought avoidance (Balibrea Lara et al, 2004;Albacete et al, 2015).…”