Vitis Flower Sex Specification Acts Downstream and Independently of the ABCDE Model Genes

Abstract

The most discriminating characteristic between the cultivated Vitis vinifera subsp. vinifera and the wild-form Vitis vinifera subsp. sylvestris is their sexual system. Flowers of cultivars are mainly hermaphroditic, whereas wild plants have female and male individuals whose flowers follow a hermaphroditic pattern during early stages of development and later develop non-functional reproductive organs. In angiosperms, the basic developmental system for floral organ identity is explained by the ABCDE model. This model postulates that regulatory gene functions work in a combinatorial way to confer organ identity in each whorl. In wild Vitis nothing is known about the function and expression profile of these genes. Here we show an overall view of the temporal and spatial expression pattern of the ABCDE genes as well as the pattern of VviSUPERMAN that establishes a boundary between the stamen and the carpel whorls, in the male, female and complete flower types. The results show a similar pattern in Vitis species suggesting that the pathway leading to unisexuality acts independently and/or downstream of B- and C- function genes.

Genomics of Flower Identity in Grapevine (Vitis vinifera L.)

“…In stamens (anthers and filaments) and in the carpel, VviAP1 was almost absent and therefore consistent with mutually repressive activity of the A- and C-class genes (Jack, 2004). Our results are partially in contraposition with that observed by Coito et al (2018), who evaluated the spatiotemporal expression of the same gene in male female and perfect grapevine flowers. Surprisingly, in that study, VviAP1 expression was barely detected in the sepal and petal regions and restricted to the inner part of the flower.…”

“…The latter was not considered in the present study since it does not encode a MADS-box TF. APETALA1 ( AP1 ) has two main functions: the first is to specify the identity of sepals (first whorl), when expressed alone, and petals (second whorl), when expressed in combination with the B-class genes APETALA3 ( AP3 ) and PISTILLATA (PI; Jack, 2004); the second function is to repress the C-class genes in these whorls (Coito et al, 2018). The putative ortholog of Arabidopsis AP1 was isolated in grapevine ( VAP1 ) (Calonje et al, 2004) and corresponds to the gene VviAP1 (VIT_01s0011g00100) based on a recent MADS-box classification (Grimplet et al, 2016).…”

“…In grapevine, three orthologs of B-function genes have been characterized and correspond to VviPI (VIT_18s0001g01760), VviAP3a (VIT_18s0001g13460), and VviAP3b (VIT_04s0023g02820) according to Grimplet et al (2016). In reality, based on phylogenetic analyses (Poupin et al, 2007; Coito et al, 2018), these genes cluster in three different clades: PI, AP3 , and TM6 , respectively. While VviPI , corresponding to VvMADS9 and/or VvPI (Sreekantan et al, 2006; Poupin et al, 2007), forms a clearly separate clade, namely, the PI clade (Poupin et al, 2007; Coito et al, 2018), VviAP3a and VviAP3b , previously designated VvAP3 and VvTM6 , respectively (Poupin et al, 2007; Table 1), present differences at the level of specific C-terminal motifs (Vandenbussche et al, 2003).…”

“…The highest VviPI, VviAP3a , and VviAP3b transcript levels were detected in the cap and stamen (anther and filament) tissues. Regarding VviAP3a , previous studies in a hermaphroditic variety of V. vinifera (Poupin et al, 2007), showed that the expression of this gene is restricted to petals and stamens, whereas in situ hybridization experiments indicated that the VviAP3a transcripts also localize in the carpels but are limited to early stages of flower development (Coito et al, 2018). In reality, a discrete expression of VviAP3a was also detected in carpels and embryos in our analysis.…”

“…In more detail, the A-class genes specify the identity of the sepals (first whorl) when expressed alone and the petals (second whorl), when expressed in combination with the B-class genes (Jack, 2004). Moreover, they were found to repress the C-class genes in these whorls (Coito et al, 2018). The C-class genes alone specify the carpel identity, whereas in combination with some B-genes, they specify the stamen identity (Coen and Meyerowitz, 1991).…”