Physiological and molecular insights into alternate bearing in mango using next-generation sequencing approaches

The productivity of the mango crop in India is hindered by many factors, one of the most important factors is our limited understanding of the genomic complexities behind the regular versus alternate bearing habit of fruit. In this study, we quantified carbohydrate fractions, protein content, and macro- and micronutrient storage pools together with their transportation and contributions to a regular bearing variety, Totapuri, and to an alternate-bearer, Bombay Green during the 'off' year. RNA-sequencing was used to assess gene expression dynamics between buds and flowers of these varieties. Differential pathway analysis showed the greatest number of differentially expressed genes in metabolic processes, followed by oxidoreductase, hormone, oxidative stress, starvation, alternate bearing, flowering, meristem, and cellular component pathways. Bioinformatics analysis showed that, among 15 highly differentially expressed genes between varieties representing alternate bearing, hormone, and carbohydrate metabolism pathways, 12 were up-regulated in Totapuri and 3 in Bombay Green, and this was confirmed by qRT-PCR. In addition, 202 single-nucleotide polymorphisms were identified in 32 genes related to alternate bearing. Our results confirmed the strong ability of reproductive buds to import sugars, proteins, and starch in the regular-bearer variety, thereby enhancing flowering and fruiting during 'off' years. Thus, our study shows a potential role for the mineral nutrient and biochemical constituents of buds and leaves in determining the regular versus alternate bearing fruiting habit in mango.