The AINTEGUMENTA genes, MdANT1 and MdANT2, are associated with the regulation of cell production during fruit growth in apple (Malus × domestica Borkh.)

Abstract

BackgroundFruit growth in apple (Malus × domestica Borkh.) is mediated by cell production and expansion. Genes involved in regulating these processes and thereby fruit growth, are not well characterized. We hypothesized that the apple homolog(s) of AINTEGUMENTA (ANT), an APETALA2–repeat containing transcription factor, regulates cell production during fruit growth in apple.ResultsTwo ANT genes, MdANT1 and MdANT2, were isolated from apple and their expression was studied during multiple stages of fruit development. MdANT1 and MdANT2 expression was high during early fruit growth coincident with the period of cell production, rapidly declined during exit from cell production, and remained low during the rest of fruit development. The effects of increase in carbohydrate availability during fruit growth were characterized. Increase in carbohydrate availability enhanced fruit growth largely through an increase in cell production. Expression of MdANT1 and MdANT2 increased sharply by up to around 5-fold in response to an increase in carbohydrate availability. Expression of the ANT genes was compared across two apple genotypes, ‘Gala’ and ‘Golden Delicious Smoothee’ (GS), which differ in the extent of fruit growth, largely due to differences in cell production. In comparison to ‘Gala’, the larger fruit-size genotype, GS, displayed higher levels and a longer duration of MdANT1 and MdANT2 expression. Expression of the ANTs and cell cycle genes in the fruit core and cortex tissues isolated using laser capture microdissection was studied. During early fruit growth, expression of the MdANTs was higher within the cortex, the tissue that constitutes the majority of the fruit. Additionally, MdANT1 and MdANT2 expression was positively correlated with that of A- and B-type CYCLINS, B-type CYCLIN-DEPENDENT-KINASES (CDKBs) and MdDEL1.ConclusionsMultiple lines of evidence from this study suggest that MdANT1 and MdANT2 regulate cell production during fruit growth in apple. ANTs may coordinate the expression of cell proliferation genes and thereby affect the competence of cells for cell production during fruit growth. Together, data from this study implicate MdANT1 and MdANT2 in the regulation of fruit growth in apple.

Higher growth of the apple (Malus × domestica Borkh.) fruit cortex is supported by resource intensive metabolism during early development

“…Cortex growth during EFD was > 5fold higher than that in the pith. Majority of cortex growth during EFD is associated with rapid cell production [9,10,28]. Hence, higher cortex growth was likely achieved through greater cell production than that in the pith.…”

“…1). Fruit load reduction enhances early fruit growth by increasing cell production [9,10,28]. Hence, additional resources translocated into the fruit due to sink-removal [30,31] are allocated primarily to enhancing cell production allowing for greater cortex growth.…”

“…Growth during MFD is primarily mediated by postmitotic cell expansion [9,10,28] and likely facilitated by metabolite accumulation in the vacuole. Differential metabolic activities across fruit tissues apparent during this period were largely related to C storage (Fig.…”

“…This was likely supported by higher C partitioning to the cortex owing to its greater sink size. Cell production, a major resource sink, ceases prior to MFD and growth is mediated largely by post-mitotic cell expansion [10,28,49].…”

“…Early fruit growth involves intensive cell production (generation of new cells in a population through cell division) [7], and extends from~8 until 30 days after full bloom (DAFB) [8,9]. This is followed by mid-and late-fruit growth which is linear and where the largest increase in size is achieved through extensive cell expansion by over 1000-fold [8,10]. This period may extend until 120-180 DAFB.…”