Fruit Development in Ficus carica L.: Morphological and Genetic Approaches to Fig Buds for an Evolution From Monoecy Toward Dioecy

Abstract

The mechanism behind the bud evolution towards breba or main crop in Ficus carica L. is uncertain. Anatomical and genetic studies may put a light on the possible similarities/ differences between the two types of fruits. For this reason, we collected complimentary data from anatomical, X-ray imaging, and genetic techniques. The RNA seq together with structural genome annotation allowed the prediction of 34,629 known genes and 938 novel protein-coding genes. Transcriptome analysis of genes during bud differentiation revealed differentially expressed genes in two fig varieties (Dottato and Petrelli) and in breba and main crop. We chose Dottato and Petrelli because the first variety does not require pollination to set main crop and the latter does; moreover, Petrelli yields many brebas whereas Dottato few. Of the 1,615 and 1,904 loci expressed in Dottato and Petrelli, specifically in breba or main crop, respectively, only 256 genes appeared to be transcripts in both varieties. The buds of the two fig varieties were observed under optical microscope and using 3D X-ray tomography, highlighting differences mainly related to the stage of development. The X-ray images of buds showed a great structural similarity between breba and main crop during the initial stages of development. Analysis at the microscope indicated that inflorescence differentiation of breba was split in two seasons whereas that of main crop started at the end of winter of season 2 and was completed within 2 to 3 months. The higher expression of floral homeotic protein AGAMOUS in breba with respect to main crop, since this protein is required for normal development of stamens and carpels in the flower, may indicate an original role of these fruits for staminate flowers production for pollination of the main crop, as profichi in the caprifig. Several genes related to auxin (auxin efflux carrier, auxin response factor, auxin binding protein, auxin responsive protein) and to GA synthesis (GA20ox) were highly expressed in brebas with respect to main crop for the development of this parthenocarpic fruit.

AGAMOUS Gene as a New Sex-Identification Marker in Fig (Ficus carica L.) Is More Efficient Than RAN1

“…In practice, only female fig trees are vegetatively propagated and grown for fig production. As pollination is required by some types of female fig cultivars, and has a positive effect on fruit quality and storability, selected male fig cultivars are used to provide pollen ( Lama et al, 2020 ; Marcotuli et al, 2020 ). Sex identification and understanding the mechanism of sex evolution of fig trees are of obvious value to breeding and crop improvement.…”

“…A recent publication recruited two fig AG genes (seq00824 and seq00026) by blasting MnAG against the “Horaishi” draft genome. Expression of both genes was reported to be much higher in breba (spring fruit) than in the main crop (autumn fruit) ( Marcotuli et al, 2020 ). However, only one conserved AG gene was found in our study.…”

“…Upon ripening, the long-styled female flowers (pistils) develop inside the syconium, making up most of the edible part of the fruit ( Stover et al, 2007 ). The caprifig is not usually edible, but stamens growing inside the syconia produce pollen, and the quality and storability of female fig fruit improve after pollination ( Lama et al, 2020 ; Marcotuli et al, 2020 ). In addition, there are short-styled female flowers (galls) in the syconia of caprifigs that can serve as hosts for fig-wasp ( Blastophaga psenes L.) larvae ( Gu and Yang, 2013 ; Zhang et al, 2020 ; Wang et al, 2021 ).…”

Do Pollination and Pollen Sources Affect Fig Seed Set and Quality? First Attempt Using Chemical and Vibrational Fingerprints Coupled with Chemometrics

“…is particular aspect divides female figs into three types. e first one is called common figs, which do not require caprification and can yield one (unifera variety) or two (bifera variety) crops [6]. e second is known as Smyrna-type figs, which require pollen from the male tree called caprifig.…”

“…Furthermore, fig seeds oil was reported to have a higher desaturation rate and a significant phenotypic effect [14,15]. Basically, as pollination is mainly involved in seeds formation [6], the main effect probably occurs over the attributes of seeds and, subsequently, the whole fruit quality. In this sense, the investigation of the caprification and source pollen effect on fresh figs must pass through its seeds' chemical and lipochemical attributes.…”