1 Horticultural Reviews, Volume 33, Edited by Jules Janick ISBN 978-0-471-73214-3 © 2007 John Wiley & Sons, Inc. *I thank R. A. Martin and A. G. Seal for reading parts of the manuscript, F. A. Gunson and I. J. Warrington for editing the entire manuscript, S. Cookson for preparing Fig. 1.1, and B. Shaw and M. Heffer for preparing the plates. The preparation of this review was supported in part by the NZ Foundation for Science Research and Technology C06X0006.

Genetic Resources of Kiwifruit: Domestication and Breeding

MADS-box genes similar to Arabidopsis SHORT VEGETATIVE PHASE (SVP) have been implicated in the regulation of flowering in annual species and bud dormancy in perennial species. Kiwifruit (Actinidia spp.) are woody perennial vines where bud dormancy and out-growth affect flower development. To determine the role of SVP-like genes in dormancy and flowering of kiwifruit, four MADS-box genes with homology to Arabidopsis SVP, designated SVP1, SVP2, SVP3, and SVP4, have been identified and analysed in kiwifruit and functionally characterized in Arabidopsis. Phylogenetic analysis indicate that these genes fall into different sub-clades within the SVP-like gene group, suggesting distinct functions. Expression was generally confined to vegetative tissues, and increased transcript accumulation in shoot buds over the winter period suggests a role for these genes in bud dormancy. Down-regulation before flower differentiation indicate possible roles as floral repressors. Over-expression and complementation studies in Arabidopsis resulted in a range of floral reversion phenotypes arising from interactions with Arabidopsis MADS-box proteins, but only SVP1 and SVP3 were able to complement the svp mutant. These results suggest that the kiwifruit SVP-like genes may have distinct roles during bud dormancy and flowering.

Conservation and divergence of four kiwifruit SVP-like MADS-box genes suggest distinct roles in kiwifruit bud dormancy and flowering

Free to read at publisher FLOWERING LOCUS T (FT) and CENTRORADIALIS (CEN) homologs have been implicated in regulation of growth, determinacy and flowering. The roles of kiwifruit FT and CEN were explored using a combination of expression analysis, protein interactions, response to temperature in high-chill and low-chill kiwifruit cultivars and ectopic expression in Arabidopsis and Actinidia. The expression and activity of FT was opposite from that of CEN and incorporated an interaction with a FLOWERING LOCUS D (FD)-like bZIP transcription factor. Accumulation of FT transcript was associated with plant maturity and particular stages of leaf, flower and fruit development, but could be detected irrespective of the flowering process and failed to induce precocious flowering in transgenic kiwifruit. Instead, transgenic plants demonstrated reduced growth and survival rate. Accumulation of FT transcript was detected in dormant buds and stem in response to winter chilling. In contrast, FD in buds was reduced by exposure to cold. CEN transcript accumulated in developing latent buds, but declined before the onset of dormancy and delayed flowering when ectopically expressed in kiwifruit. Our results suggest roles for FT, CEN and FD in integration of developmental and environmental cues that affect dormancy, budbreak and flowering in kiwifruit.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.12162

Homologs of FT, CEN and FD respond to developmental and environmental signals affecting growth and flowering in the perennial vine kiwifruit

Mannan transglycosylase is a novel cell wall enzyme activity acting on mannan-based plant polysaccharides in primary cell walls of monocotyledons and dicotyledons. The enzyme activity was detected by its ability to transfer galactoglucomannan (GGM) polysaccharides to tritium-labelled GGM-derived oligosaccharides generating tritium-labelled GGM polysaccharides. Mannan transglycosylase was found in a range of plant species and tissues. High levels of the enzyme activity were present in flowers of some kiwifruit (Actinidia) species and in ripe tomato (Solanum lycopersicum L.) fruit. Low levels were detected in mature green tomato fruit and activity increased during tomato fruit ripening up to the red ripe stage. Essentially all activity was found in the tomato skin and outermost 2 mm of tissue. Mannan transglycosylase activity in tomato skin and outer pericarp is specific for mannan-based plant polysaccharides, including GGM, galactomannan, glucomannan and mannan. The exact structural requirements for valid acceptors remain to be defined. Nevertheless, a mannose residue at the second position of the sugar chain and the absence of a galactose substituent on the fourth residue (counting from the non-reducing end) appear to be minimal requirements. Mannan-based polysaccharides in the plant cell wall may have a role analogous to that of xyloglucans, introducing flexibility and forming growth-restraining networks with cellulose. Thus mannan transglycosylase and xyloglucan endotransglycosylase, the only other known transglycosylase activity in plant cell walls, may both be involved in remodelling and refining the cellulose framework in developmental processes throughout the life of a plant.

Mannan transglycosylase: a novel enzyme activity in cell walls of higher plants.

Previous studies have established that chloroplasts are inherited paternally in Actinidia interspecific crosses. However, fertilisation problems in interspecific crosses may affect the transmission of organelles. Six female clones, i.e. ‘Abbott’, ‘Bruno’, ‘Greensill’, ‘Hayward’, ‘Jones’, ‘Monty’, and four male clones were used to identify cpDNA polymorphisms within the cultivated kiwifruit species A. deliciosa. The restriction patterns by HpaII of a chloroplast fragment amplified by PCR with a pair of universal primers revealed a polymorphism at the intraspecific level. The inheritance of cpDNA in 143 seedlings from three intraspecific crosses in kiwifruit (Actinidia deliciosa) was studied. All offspring displayed the restriction pattern of the paternal parent, indicating that maternal inheritance of cpDNA in kiwifruit is rare at best. Strict maternal inheritance of mtDNA was confirmed in the same crosses used to investigate cpDNA transmission. Studies of cytoplasmic inheritance in the Actinidia genus represent to date the best documented report of differential organelle inheritance of cpDNA and mtDNA in angiosperms.

J.A. Grant

Papers

Initiation and development of pistillate flowers in Actinidia chinensis