RESUMEN

Breadfruit (Artocarpus altilis) is a traditional fruit tree of 15-30 m height in the tropics. The presence of size-controlling rootstock in the species is not known. A small tropical tree species, lakoocha (Artocarpus lakoocha), was recently identified as a potential vigor-controlling rootstock, conferring over a 65% reduction in breadfruit tree height. To better understand the intriguing scion/rootstock interactions involved in dwarfing, we investigate flavonoid accumulation and its regulation in breadfruit scions in response to different rootstocks. To this end, we isolated a chalcone synthase cDNA, AaCHS, and a full-length bifunctional dihydroflavonol 4-reductase cDNA, AaDFR, from breadfruit scion stems. The expression of both AaCHS and AaDFR genes was examined over the period of 16 to 24 months following grafting. During the development of the dwarf phenotype, breadfruit scion stems on lakoocha rootstocks display significant increases in total flavonoid content, and show upregulated AaCHS expression when compared with those on self-grafts and non-grafts. There is a strong, positive correlation between the transcript levels of AaCHS and total flavonoid content in scion stems. The transcript levels of AaDFR are not significantly different across scions on different rootstocks. This work provides insights into the significance of flavonoid biosynthesis in rootstock-induced breadfruit dwarfing.

RESUMEN

Breadfruit is an underutilized but highly nutritive crop containing complex carbohydrates while being low in fat. It is also a good source of essential amino acids (leucine, isoleucine, and valine). With a better understanding of breadfruit's morphology, its potential as a global solution to food security has been gaining popularity. Breadfruit has been forecasted to have a larger amount of suitable cultivable land area compared to major crops such as rice and wheat, making its cultivation more desirable. Due to its highly perishable nature, good post-harvesting and post-processing practices are essential to extend the shelf life of breadfruit for global transportation and consumption. This paper aims to provide a comprehensive review on various processing methods of flour and starch, nutritional significance and new food applications of this novel food staple. In this review, the effects of the different processing and post-processing methods of breadfruit flour and starch have been described, and the nutritional composition and application of breadfruit flour as an ingredient replacer in various food applications have been discussed. It is vital to understand the processing and post-processing methods of breadfruit flour to enhance its shelf-life, physicochemical and functional properties. Furthermore, a compilation of novel food applications has been done to promote its use in the food industry. In conclusion, breadfruit flour and starch are highly versatile for use in numerous food products with added health benefits.

RESUMEN

BACKGROUND: Breadfruit (Artocarpus altilis) is a traditional staple tree crop throughout the tropics. Through interspecific grafting, a dwarf phenotype with over 50% reduction in plant height was identified when marang (Artocarpus odoratissimus) rootstocks were used. However, the molecular mechanism underlying the rootstock-induced breadfruit dwarfing is poorly understood. RESULTS: An RNA-sequencing study of breadfruit scions at 22 months after grafting identified 5409 differentially expressed genes (DEGs) of which 2069 were upregulated and 3339 were downregulated in scion stems on marang rootstocks compared to those on self-graft. The DEGs were predominantly enriched for biological processes involved in carbon metabolism, cell wall organization, plant hormone signal transduction and redox homeostasis. The down-regulation of genes encoding vacuolar acid invertases and alkaline/neutral invertases, was consistent with the decreased activity of both enzymes, accompanying with a higher sucrose but lower glucose and fructose levels in the tissues. Key genes of biosynthetic pathways for amino acids, lipids and cell wall were down regulated, reflecting reduction of sucrose utilisation for stem growth on dwarfing rootstocks. Genes encoding sugar transporters, amino acid transporters, choline transporters, along with large number of potassium channels and aquaporin family members were down-regulated in scion stems on marang rootstocks. Lower activity of plasma membrane H+-ATPase, together with the predominance of genes encoding expansins, wall-associated receptor kinases and key enzymes for biosynthesis and re-modelling of cellulose, xyloglucans and pectins in down-regulated DGEs suggested impairment of cell expansion. Signalling pathways of auxin and gibberellin, along with strigolacton and brassinosteroid biosynthetic genes dominated the down-regulated DEGs. Phenylpropanoid pathway was enriched, with key lignin biosynthetic genes down-regulated, and flavonoid biosynthetic genes upregulated in scions on marang rootstocks. Signalling pathways of salicylic acid, jasmonic acid, ethylene and MAPK cascade were significantly enriched in the upregulated DEGs. CONCLUSIONS: Rootstock-induced disruption in pathways regulating nutrient transport, sucrose utilisation, cell wall biosynthesis and networks of hormone transduction are proposed to impair cell expansion and stem elongation, leading to dwarf phenotype in breadfruit scions. The information provides opportunity to develop screening strategy for rootstock breeding and selection for breadfruit dwarfing.

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RESUMEN

Breadfruit (Artocarpus altilis) is a traditional staple tree crop throughout the tropics. The species is an evergreen tree 15-20 m; there are currently no size-controlling rootstocks within the species. Through interspecific grafting, a dwarf phenotype was identified in breadfruit plants growing on Marang (Artocarpus odoratissimus) rootstocks, which displayed ~60% reduction in plant height with ~80% shorter internodes. To gain insight into the molecular mechanism underlying rootstock-induced dwarfing, we investigated the involvement of gibberellin (GA) in reduction of stem elongation. Expression of GA metabolism genes was analysed in the period from 18 to 24 months after grafting. In comparison to self-graft and non-graft, scion stems on marang rootstocks displayed decrease in expression of a GA biosynthetic gene, AaGA20ox3, and increase in expression of a GA catabolic genes, AaGA2ox1, in the tested 6-month period. Increased accumulation of DELLA proteins (GA-signalling repressors) was found in scion stems growing on marang rootstocks, together with an increased expression of a DELLA gene, AaDELLA1. Exogenous GA treatment was able to restore the stem elongation rate and the internode length of scions growing on marang rootstocks. The possibility that GA deficiency forms a component of the mechanism underlying rootstock-induced breadfruit dwarfing is discussed.

RESUMEN

Breadfruit (Artocarpus altilis) is primarily grown as a staple tree crop for food security in Oceania. Significant wind damage has driven interest in developing its dwarfing rootstocks. Due to the predominantly vegetative propagation of the species, grafting onto interspecific seedlings is an approach to identifying dwarfing rootstocks. However, grafting of breadfruit onto unrelated Artocarpus species has not been investigated. Here we first report the success of breadfruit grafting onto interspecific rootstocks, marang (A. odoratissimus) and pedalai (A. sericicarpus). To address the low graft survival, we investigated the relationship of plasma membrane (PM) H+ -ATPase activity to graft success. We provide the first evidence for a positive correlation between PM H+ -ATPase activity and graft survival. The graft unions of successful grafts had higher PM H+ -ATPase activity compared to those of failed grafts. Rootstocks with low PM H+ -ATPase activity in leaf microsomes before grafting had lower graft survival than those with high enzyme activity, with graft success of 10% versus 60% and 0% versus 30% for marang and pedalai rootstocks, respectively. There was a positive correlation between graft success and the PM H+ -ATPase activity measured from the rootstock stem microsomes 2 months after grafting [marang, r(7) = 0.9203, P = 0.0004; pedalai (r(7) = 0. 8820, P = 0.0017]. Removal of scion's own roots decreased the leaf PM H+ -ATPase activity of grafted plants regardless of the final graft outcome. Recovery of the enzyme activity was only found in the successful grafts. The function of PM H+ -ATPase in graft union development and graft success improvement is discussed.

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RESUMEN

Breadfruit (Artocarpus altilis) is a traditional staple tree crop in the Oceania. Susceptibility to windstorm damage is a primary constraint on breadfruit cultivation. Significant tree loss due to intense tropical windstorm in the past decades has driven a widespread interest in developing breadfruit with dwarf stature. Gibberellin (GA) is one of the most important determinants of plant height. GA 2-oxidase is a key enzyme regulating the flux of GA through deactivating biologically active GAs in plants. As a first step toward understanding the molecular mechanism of growth regulation in the species, we isolated a cohort of four full-length GA2-oxidase cDNAs, AaGA2ox1- AaGA2ox4 from breadfruit. Sequence analysis indicated the deduced proteins encoded by these AaGA2oxs clustered together under the C19 GA2ox group. Transcripts of AaGA2ox1, AaGA2ox2 and AaGA2ox3 were detected in all plant organs, but exhibited highest level in source leaves and stems. In contrast, transcript of AaGA2ox4 was predominantly expressed in roots and flowers, and displayed very low expression in leaves and stems. AaGA2ox1, AaGA2ox2 and AaGA2ox3, but not AaGA2ox4 were subjected to GA feedback regulation where application of exogenous GA3 or gibberellin biosynthesis inhibitor, paclobutrazol was shown to manipulate the first internode elongation of breadfruit. Treatments of drought or high salinity increased the expression of AaGA2ox1, AaGA2ox2 and AaGA2ox4. But AaGA2ox3 was down-regulated under salt stress. The function of AaGA2oxs is discussed with particular reference to their role in stem elongation and involvement in abiotic stress response in breadfruit.

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