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Fruit growth depends on highly coordinated hormonal activities. The phytohormone gibberellin (GA) promotes growth by triggering degradation of the growth-repressing DELLA proteins; however, the extent to which such proteins contribute to GA-mediated fruit development remains to be clarified. Three new plum genes encoding DELLA proteins, PslGAI, PslRGL and PslRGA were isolated and functionally characterized. Analysis of expression profile during fruit development suggested that PslDELLA are transcriptionally regulated during flower and fruit ontogeny with potential positive regulation by GA and ethylene, depending on organ and developmental stage. PslGAI and PslRGL deduced proteins contain all domains present in typical DELLA proteins. However, PslRGA exhibited a degenerated DELLA domain and subsequently lacks in GID1–DELLA interaction property. PslDELLA–overexpression in WT Arabidopsis caused dramatic disruption in overall growth including root length, stem elongation, plant architecture, flower structure, fertility, and considerable retardation in development due to dramatic distortion in GA-metabolic pathway. GA treatment enhanced PslGAI/PslRGL interaction with PslGID1 receptors, causing protein destabilization and relief of growth-restraining effect. By contrast, PslRGA protein was not degraded by GA due to its inability to interact with PslGID1. Relative to other PslDELLA–mutants, PslRGA–plants displayed stronger constitutive repressive growth that was irreversible by GA application. The present results describe additional complexities in GA-signalling during plum fruit development, which may be particularly important to optimize successful reproductive growth. [ABSTRACT FROM AUTHOR]

Pear (Pyrus communis L.) are climacteric fruit: their ripening is associated with a burst of autocatalytic ethylene production. Some late pear cultivars, such as Passe‐Crassane (PC) require a long (80 d) chilling treatment before the fruit will produce autocatalytic ethylene and ripen. As the cold requirement is linked to the capacity to respond to ethylene (or its analogue, propylene), three pear cDNAs homologous to the Arabidopsis ethylene receptor genes At‐ETR1, At‐ERS1, and At‐ETR2, designated Pc‐ETR1a (AF386509), Pc‐ERS1a (AF386515), and Pc‐ETR5 (AF386511), respectively, have been isolated. A pear homologue of the Arabidopsis ethylene signal transduction pathway gene At‐CTR1, called Pc‐CTR1 (AF386508) has also been isolated. The search of the genomic sequences for Pc‐ETR1a and Pc‐ERS1a resulted in the isolation of four related genomic clones Pc‐DETR1a (AF386525), Pc‐DETR1b (AF386520), Pc‐DERS1a (AF386517), and Pc‐DERS1b (AF386522). Analysis of transcript levels for the four cDNAs in PC and pear fruit genotypes with little or no cold requirement revealed that Pc‐ETR1a expression increased during chilling treatment, and Pc‐ETR1a, Pc‐ERS1a, Pc‐ETR5, and Pc‐CTR1 expression increased during fruit ripening and after ethylene treatment. Whether the differences in the ethylene response elements studied here are the cause or an effect of the cold requirement in PC fruit is discussed. [ABSTRACT FROM PUBLISHER]

The apical hook of dark-grown dicotyledonous plants results from asymmetric growth of the inner and outer sides of the upper part of the hypocotyl. This protective structure prevents damage of the shoot apical meristem and the young leaves as the seedling pushes through the soil. HOOKLESS (HLS1) of Arabidopsis was recognised as an ethylene response gene whose product is required for hook formation. We cloned two cDNAs from tomato, Sl- HLS1 and Sl- HLS2 , and showed through the complementation of the Arabidopsis hls1 mutant that the encoded proteins are functional orthologs of At-HLS1. The genomic clones of Sl- HLS1 and Sl- HLS2 showed similar structure with two introns and three exons. While the data indicate complete functional redundancy between the two tomato HLS genes, only the expression of Sl- HLS2 is regulated by ethylene and auxin and the ethylene-induced expression of Sl- HLS2 is localised in the outer side of the hook while the auxin-responsive expression is not restricted to a specific side of the hook. 1-MCP, an inhibitor of ethylene signalling, inhibited auxin-enhanced accumulation of Sl- HLS2 mRNA in the apical hook suggesting that regulation of Sl- HLS2 by auxin is ethylene-dependent. The overexpression of tomato Sl- HLS1 and Sl- HLS2 in Arabidopsis confers hypersensitivity to ethylene. The data presented bring further insight into the complex ethylene-auxin interplay in hook formation. [ABSTRACT FROM AUTHOR]