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SUMMARY: Auxin plays an essential role in plant growth and development, particularly in fruit development. The YUCCA (YUC) genes encode flavin monooxygenases that catalyze a rate‐limiting step in auxin biosynthesis. Mutations that disrupt YUC gene function provide useful tools for dissecting general and specific functions of auxin during plant development. In woodland strawberry (Fragaria vesca), two ethyl methanesulfonate mutants, Y422 and Y1011, have been identified that exhibit severe defects in leaves and flowers. In particular, the width of the leaf blade is greatly reduced, and each leaflet in the mutants has fewer and deeper serrations. In addition, the number and shape of the floral organs are altered, resulting in smaller fruits. Mapping by sequencing revealed that both mutations reside in the FveYUC4 gene, and were therefore renamed as yuc4‐1 and yuc4‐2. Consistent with a role for FveYUC4 in auxin synthesis, free auxin and its metabolites are significantly reduced in the yuc4 leaves and flowers. This role of FveYUC4 in leaf and flower development is supported by its high and specific expression in young leaves and flower buds using GUS reporters. Furthermore, germline transformation of pYUC4::YUC4, which resulted in elevated expression of FveYUC4 in yuc4 mutants, not only rescued the leaf and flower defects but also produced parthenocarpic fruits. Taken together, our data demonstrate that FveYUC4 is essential for leaf and flower morphogenesis in woodland strawberry by providing auxin hormone at the proper time and in the right tissues. Significance Statement: Mutants of the auxin biosynthesis gene FveYUC4 have been identified in woodland strawberry, demonstrating the importance of local auxin biosynthesis in regulating leaf shape and floral organ formation. Germline transformation of pYUC4::YUC4 can not only rescue the leaf and flower defects of yuc4, but also produces pollination‐independent fruits due to increased expression of FveYUC4, a candidate gene for the introduction of parthenocarpy in strawberry. [ABSTRACT FROM AUTHOR]

SUMMARY: Soluble sugars play an important role in plant growth, development and fruit quality. Pear fruits have demonstrated a considerable improvement in sugar quality during their long history of selection. However, little is known about the underlying molecular mechanisms accompanying the changes in fruit sugar content as a result of selection by horticulturists. Here, we identified a calcium‐dependent protein kinase (PbCPK28), which is located on LG15 and is present within a selective sweep region, thus linked to the quantitative trait loci for soluble solids. Association analysis indicates that a single nucleotide polymorphism‐13 variation (SNP13T/C) in the PbCPK28 regulatory region led to fructose content diversity in pear. Elevated expression of PbCPK28 resulted in significantly increased fructose levels in pear fruits. Furthermore, PbCPK28 interacts with and phosphorylates PbTST4, a proton antiporter, thereby coupling the sugar import into the vacuole with proton export. We demonstrated that residues S277 and S314 of PbTST4 are crucial for its function. Additionally, PbCPK28 interacts with and phosphorylates the vacuolar hydrogen proton pump PbVHA‐A1, which could provide proton motive forces for PbTST4. We also found that the T11 and Y120 phosphorylation sites in PbVHA‐A1 are essential for its function. Evolution analysis and yeast‐two‐hybrid results support that the CPK‐TST/CPK‐VHA‐A regulatory network is highly conserved in plants, especially the corresponding phosphorylation sites. Together, our work identifies an agriculturally important natural variation and an important regulatory network, allowing genetic improvement of fruit sugar contents in pears through modulation of PbCPK28 expression and phosphorylation of PbTST4 and PbVHA‐A1. Significance Statement: The changes in fruit sugars are a result of selection by early horticulturists. However, little is known about the underlying molecular mechanisms conferring these changes. Here, we identified a domesticated calcium‐dependent protein kinase gene, PbCPK28, that interacted with and phosphorylates the H+/sugar antiporter PbTST4 and vacuolar hydrogen proton pump PbVHA‐A1 to increase the sugar content of pear fruits. Further results showed that the CPK‐TST/CPK‐VHA‐A regulatory network is highly conserved in plants. Our findings provide new insights into the regulatory mechanism for sugar accumulation in fruits. [ABSTRACT FROM AUTHOR]

SUMMARY: Fruits represent key evolutionary innovations in angiosperms and exhibit diverse types adapted for seed dissemination. However, the mechanisms that underlie fruit type diversity are not understood. The Rosaceae family comprises many different fruit types, including 'pome' and 'drupe' fruits, and hence is an excellent family for investigating the genetic basis of fruit type specification. Using comparative transcriptomics, we investigated the molecular events that correlate with pome (apple) and drupe (peach) fleshy fruit development, focusing on the earliest stages of fruit initiation. We identified PI and TM6, MADS box genes whose expression negatively correlates with fruit flesh‐forming tissues irrespective of fruit type. In addition, the MADS box gene FBP9 is expressed in fruit‐forming tissues in both species, and was lost multiple times in the genomes of dry‐fruit‐forming eudicots including Arabidopsis. Network analysis reveals co‐expression between FBP9 and photosynthesis genes in both apple and peach, suggesting that FBP9 and photosynthesis may both promote fleshy fruit development. The large transcriptomic datasets at the earliest stages of pome and drupe fruit development provide rich resources for comparative studies, and the work provides important insights into fruit‐type specification. Significance Statement: Rose family of plants exhibit a diverse array of fruit types when fruit flesh develops from different floral parts. Through comparative transcriptomic analyses of carefully dissected and staged fruit tissues from apple (a pome) and peach (a drupe), candidate regulators of fleshy fruit identity are identified and a step‐wise specification of fruit type via MADS box genes and phytohormones is proposed. [ABSTRACT FROM AUTHOR]

Alternative splicing ( AS) is a key post-transcriptional regulatory mechanism, yet little information is known about its roles in fruit crops. Here, AS was globally analyzed in the wild strawberry Fragaria vesca genome with RNA-seq data derived from different stages of fruit development. The AS landscape was characterized and compared between the single-molecule, real-time ( SMRT) and Illumina RNA-seq platform. While SMRT has a lower sequencing depth, it identifies more genes undergoing AS (57.67% of detected multiexon genes) when it is compared with Illumina (33.48%), illustrating the efficacy of SMRT in AS identification. We investigated different modes of AS in the context of fruit development; the percentage of intron retention ( IR) is markedly reduced whereas that of alternative acceptor sites ( AA) is significantly increased post-fertilization when compared with pre-fertilization. When all the identified transcripts were combined, a total of 66.43% detected multiexon genes in strawberry undergo AS, some of which lead to a gain or loss of conserved domains in the gene products. The work demonstrates that SMRT sequencing is highly powerful in AS discovery and provides a rich data resource for later functional studies of different isoforms. Further, shifting AS modes may contribute to rapid changes of gene expression during fruit set. [ABSTRACT FROM AUTHOR]