Overexpression of the persimmon abscisic acid β‐glucosidase gene (DkBG1) alters fruit ripening in transgenic tomato

β‐Glucosidases (BG) are present in many plant tissues. Among these, abscisic acid (ABA) β‐glucosidases are thought to take part in the adjustment of cellular ABA levels, however the role of ABA‐BG in fruits is still unclear. In this study, through RNA‐seq analysis of persimmon fruit, 10 full‐length DkBG genes were isolated and were all found to be expressed. In particular, DkBG1 was highly expressed in persimmon fruits with a maximum expression 95 days after full bloom (DAFD). We verified that, in vitro, DkBG1 protein can hydrolyze ABA‐glucose ester (ABA‐GE) to release free ABA. Compared with wild‐type, tomato plants that overexpressed DkBG1 significantly upregulated the expression of ABA receptor PYL3/7 genes and showed typical symptoms of ABA hypersensitivity in fruits. DkBG1 overexpression (DkBG1‐OE) accelerated fruit ripening onset by 3–4 days by increasing ABA levels at the pre‐breaker stage and induced early ethylene release compared with wild‐type fruits. DkBG1‐OE altered the expression of ripening regulator NON‐RIPENING (NOR) and its target genes; this in turn altered fruit quality traits such as coloration. Our results demonstrated that DkBG1 plays an important role in fruit ripening and quality by adjusting ABA levels via hydrolysis of ABA‐GE.     

A biotechnology‐based male‐sterility system for hybrid seed production in tomato

Incorporating male sterility into hybrid seed production reduces its cost and ensures high varietal purity. Despite these advantages, male‐sterile lines have not been widely used to produce tomato (Solanum lycopersicum) hybrid seeds. We describe the development of a biotechnology‐based breeding platform that utilized genic male sterility to produce hybrid seeds. In this platform, we generated a novel male‐sterile tomato line by clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR‐associated protein 9 (Cas9)‐mediated mutagenesis of a stamen‐specific gene SlSTR1 and devised a transgenic maintainer by transforming male‐sterile plants with a fertility‐restoration gene linked to a seedling‐colour gene. Offspring of crosses between a hemizygous maintainer and the homozygous male‐sterile plant segregated into 50% non‐transgenic male‐sterile plants and 50% male‐fertile maintainer plants, which could be easily distinguished by seedling colour. This system has great practical potential for hybrid seed breeding and production as it overcomes the problems intrinsic to other male‐sterility systems and can be easily adapted for a range of tomato cultivars and diverse vegetable crops.     

Uncovering the evolutionary origin of blue anthocyanins in cereal grains

Functional divergence after gene duplication plays a central role in plant evolution. Among cereals, only Hordeum vulgare (barley), Triticum aestivum (wheat) and Secale cereale (rye) accumulate delphinidin‐derived (blue) anthocyanins in the aleurone layer of grains, whereas Oryza sativa (rice), Zea mays (maize) and Sorghum bicolor (sorghum) do not. The underlying genetic basis for this natural occurrence remains elusive. Here, we mapped the barley Blx1 locus involved in blue aleurone to an approximately 1.13 Mb genetic interval on chromosome 4HL, thus identifying a trigenic cluster named MbHF35 (containing HvMYB4H, HvMYC4H and HvF35H). Sequence and expression data supported the role of these genes in conferring blue‐coloured (blue aleurone) grains. Synteny analyses across monocot species showed that MbHF35 has only evolved within distinct Triticeae lineages, as a result of dispersed gene duplication. Phylogeny analyses revealed a shared evolution pattern for MbHF35 in Triticeae, suggesting that these genes have co‐evolved together. We also identified a Pooideae‐specific flavonoid 3′,5′‐hydroxylase (F3′5′H) lineage, termed here Mo_F35H2, which has a higher amino acid similarity with eudicot F3′5′Hs, demonstrating a scenario of convergent evolution. Indeed, selection tests identified 13 amino acid residues in Mo_F35H2 that underwent positive selection, possibly driven by protein thermostablility selection. Furthermore, through the interrogation of barley germplasm there is evidence that HvMYB4H and HvMYC4H have undergone human selection. Collectively, our study favours blue aleurone as a recently evolved trait resulting from environmental adaptation. Our findings provide an evolutionary explanation for the absence of blue anthocyanins in other cereals and highlight the importance of gene functional divergence for plant diversity and environmental adaptation.