Dataset Information

Expression of MdCCD7 in the scion determines the extent of sylleptic branching and the primary shoot growth rate of apple trees.

ABSTRACT: Branching has a major influence on the overall shape and productivity of a plant. Strigolactones (SLs) have been identified as plant hormones that have a key role in suppressing the outgrowth of axillary meristems. CAROTENOID CLEAVAGE DIOXYGENASE (CCD) genes are integral to the biosynthesis of SLs and are well characterized in annual plants, but their role in woody perennials is relatively unknown. We identified CCD7 and CCD8 orthologues from apple and demonstrated that MdCCD7 and MdCCD8 are able to complement the Arabidopsis branching mutants max3 and max4 respectively, indicating conserved function. RNAi lines of MdCCD7 show reduced gene expression and increased branching in apple. We performed reciprocal grafting experiments with combinations of MdCCD7 RNAi and wild-type 'Royal Gala' as rootstocks and scion. Unexpectedly, wild-type roots were unable to suppress branching in MdCCD7 RNAi scions. Another key finding was that MdCCD7 RNAi scions initiated phytomers at an increased rate relative to the wild type, resulting in a greater node number and primary shoot length. We suggest that localized SL biosynthesis in the shoot, rather than roots, controls axillary bud outgrowth and shoot growth rate in apple.

SUBMITTER: Foster TM

PROVIDER: S-EPMC5913623 | biostudies-literature | 2018 Apr

REPOSITORIES: biostudies-literature

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Expression of MdCCD7 in the scion determines the extent of sylleptic branching and the primary shoot growth rate of apple trees.

Foster Toshi M TM Ledger Susan E SE Janssen Bart J BJ Luo Zhiwei Z Drummond Revel S M RSM Tomes Sumathi S Karunairetnam Sakuntala S Waite Chethi N CN Funnell Keith A KA van Hooijdonk Ben M BM Saei Ali A Seleznyova Alla N AN Snowden Kimberley C KC

Journal of experimental botany 20180401 9

Branching has a major influence on the overall shape and productivity of a plant. Strigolactones (SLs) have been identified as plant hormones that have a key role in suppressing the outgrowth of axillary meristems. CAROTENOID CLEAVAGE DIOXYGENASE (CCD) genes are integral to the biosynthesis of SLs and are well characterized in annual plants, but their role in woody perennials is relatively unknown. We identified CCD7 and CCD8 orthologues from apple and demonstrated that MdCCD7 and MdCCD8 are abl ...[more]

PMID: 29190381

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Project description:Background and aimsShoot characteristics differ depending on the meristem tissue that they originate from and environmental conditions during their development. This study focused on the effects of plant water status on axillary meristem fate and flowering patterns along proleptic and epicormic shoots, as well as on shoot growth rates on 'Nonpareil' almond trees (Prunus dulcis). The aims were (1) to characterize the structural differences between proleptic and epicormic shoots, (2) to determine whether water deficits modify shoot structures differently depending on shoot type, and (3) to determine whether shoot structures are related to shoot growth rates.MethodsA hidden semi-Markov model of the axillary meristem fate and number of flower buds per node was built for two shoot types growing on trees exposed to three plant water status treatments. The models segmented observed shoots into successive homogeneous zones, which were compared between treatments. Shoot growth rates were calculated from shoot extension measurements made during the growing season.Key resultsProleptic shoots had seven successive homogeneous zones while epicormic shoots had five zones. Shoot structures were associated with changes in growth rate over the season. Water deficit (1) affected the occurrence and lengths of the first zones of proleptic shoots, but only the occurrence of the third zone was reduced in epicormic shoots; (2) had a minor effect on zone flowering patterns and did not modify shoot or zone composition of axillary meristem fates; and (3) reduced growth rates, although patterns over the season were similar among treatments.ConclusionsTwo meristem types, with different latency durations, produced shoots with different growth rates and distinct structures. Differences between shoot type structure responses to water deficit appeared to reflect their ontogenetic characteristics and/or resource availability for their development. Tree water deficit appeared to stimulate a more rapid progression through ontogenetic states.

Project description:Two methods were developed for the generation of cisgenic apples. Both have been successfully applied producing trees. The first method avoids the use of any foreign selectable marker genes; only the gene-of-interest is integrated between the T-DNA border sequences. The second method makes use of recombinase-based marker excision. For the first method we used the MdMYB10 gene from a red-fleshed apple coding for a transcription factor involved in regulating anthocyanin biosynthesis. Red plantlets were obtained and presence of the cisgene was confirmed. Plantlets were grafted and grown in a greenhouse. After 3 years, the first flowers appeared, showing red petals. Pollination led to production of red-fleshed cisgenic apples. The second method used the pM(arker)F(ree) vector system, introducing the scab resistance gene Rvi6, derived from apple. Agrobacterium-mediated transformation, followed by selection on kanamycin, produced genetically modified apple lines. Next, leaves from in vitro material were treated to activate the recombinase leading to excision of selection genes. Subsequently, the leaf explants were subjected to negative selection for marker-free plantlets by inducing regeneration on medium containing 5-fluorocytosine. After verification of the marker-free nature, the obtained plants were grafted onto rootstocks. Young trees from four cisgenic lines and one intragenic line, all containing Rvi6, were planted in an orchard. Appropriate controls were incorporated in this trial. We scored scab incidence for three consecutive years on leaves after inoculations with Rvi6-avirulent strains. One cisgenic line and the intragenic line performed as well as the resistant control. In 2014 trees started to overcome their juvenile character and formed flowers and fruits. The first results of scoring scab symptoms on apple fruits were obtained. Apple fruits from susceptible controls showed scab symptoms, while fruits from cisgenic and intragenic lines were free of scab.

Dataset Information

Expression of MdCCD7 in the scion determines the extent of sylleptic branching and the primary shoot growth rate of apple trees.

Publications

Expression of MdCCD7 in the scion determines the extent of sylleptic branching and the primary shoot growth rate of apple trees.

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