Annals of Botany

Carpel and fruit development genes in Solanaceae

The genetic basis underlying fruit diversity is not yet fully understood, as mainly unrelated model species have been studied. Scientists have identified in Arabidopsis major transcription factors controlling valve identity (i.e. FRUITFULL), replum development (i.e. REPLUMLESS) and the differentiation of the dehiscence zones (i.e. SHATTERPROOF, INDEHISCENT and ALCATRAZ). This gene regulatory network in other flowering plants is influenced by duplication events during angiosperm diversification.

Expression analyses of ALCATRAZ, HECATE, REPLUMLESS and SPATULA homologues in four species of Solanaceae with dry dehiscent and fleshy fruits. 
Expression analyses of ALCATRAZ, HECATE, REPLUMLESS and SPATULA homologues in four species of Solanaceae with dry dehiscent and fleshy fruits. ACTIN was used as a loading control. Expression of all homologues is shown in dissected floral organs, fruits (F1 and F2) and leaves of (A) Brunfelsia australis, (B) Nicotiana obtusifolia, (C) Capsicum annuum ‘Black Pearl’ and (D) Solanum lycopersicum‘MicroTom’. C, carpels; Fb, floral bud; F1, early stages of fruit development; F2, late stages of fruit development; L, leaves; P, petals; S, sepals; St, stamens. -C indicates the amplification reaction loaded without cDNA.

The Solanaceae are in a different family but contain many major crops. While plenty has been studied in the Solanaceae, little is known about carpel-to-fruit transformations and the genetic underpinnings of dry dehiscent fruits, fruits that split open at maturity. Most of the key regulatory genes of fruit development identified in Arabidopsis have also been studied in tomato. Ortiz-Ramírez and colleagues aimed to characterize candidate fruit development genes in the Solanaceae and compare them with those of Brassicaceae. They assessed the genetic regulatory network in fleshy berry (Solanum and Capsicum) versus dry capsule (Brunfelsia and Nicotiana) fruited species, sharing a common ancestor. The Solanaceae members exhibit a wide variety of anatomical features underlying dry and fleshy fruits, as well as a unique genetic fruit development toolkit as a result of independent gene duplication events.

Downstream FRUITFULL-SHATTERPROOF the ALCATRAZ/SPATULA as well as the REPLUMLESS genes are differentially regulated in species with berries and capsules. The study portrays a more complex genetic scenario for carpel and fruit patterning in the Solanaceae than previously suggested. The authors found the Solanaceae would have a lot more genetic redundancy when compared with Brassicaceae in all gene lineages involved in gynoecium patterning and fruit development, with the sole exception of SHP genes, which are duplicated in Brassicaceae and are single-copy in Solanaceae.

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