Search

Seeds exhibit primary dormancy to prevent germination under unfavourable conditions. Previous studies have shown that the gibberellin signalling intermediate RGA-LIKE2 (RGL2) forms a transcription factor complex with DNA-BINDING ONE ZINC FINGER6 (DOF6) in regulating seed dormancy in Arabidopsis. Using an RNA-sequencing approach, we identified MAJOR LATEX PROTEIN-LIKE PROTEIN329 (MLP329) as a downstream target of DOF6. MLP329 was found to be a positive regulator of primary seed dormancy, because freshly harvested unstratified mlp329 mutant seeds showed early germination, while unstratified transgenic seeds overexpressing MLP329 showed poor germination. MLP329 expression level was reduced in wild-type seeds upon dry storage and cold stratification. MLP329 expression level was enhanced by DOF6; however, DOF6-dependent MLP329 expression was suppressed in the presence of RGL2. MLP329 expression was enhanced in seeds treated with ABA and auxin IAA. Moreover, the mlp329 mutant seeds exhibited enhanced expression of the GA biosynthetic gene GA1 and suppression of the ABA biosynthetic gene ZEP compared to the overexpression lines. The observed suppression of DOF6-dependent MLP329 expression by RGL2 reveals a possible negative feedback mechanism to modulate seed dormancy. MLP329 also probably enhances the endogenous ABA/GA ratio to positively regulate primary seed dormancy. [ABSTRACT FROM AUTHOR]

• Variations in bloom dates among apple cultivars could be attributed to differential heat requirements. • Apple cultivars with contrasting bloom dates show distinct levels of ABA, particularly during the eco-dormancy phase. • ABA biosynthetic and catabolic genes show differential expression levels between early- and late-blooming apple cultivars. Apple production in temperate regions is continuously imperiled by spring frosts. Economic losses caused by frost damage can be enormous, and the risk of such losses is projected to rise due to global climate change. Induction of bloom delay has been suggested as a potential frost avoidance strategy. However, applicable practices toward this goal are largely lacking, primarily due to the complexity of mechanisms governing dormancy and blooming in deciduous woody perennials like pome fruits. Cultivars differing in bloom time provide a suitable platform for investigating the regulatory mechanisms of these phenological processes. In this study, we investigated the hormonal regulation of bud dormancy and blooming in two apple cultivars, 'Honeycrisp' and 'Cripps Pink', which represent late- and early-blooming apple cultivars, respectively. Our results indicated that the two cultivars showed similar chilling requirements but differed significantly in the number of growing degree hours (GDH) required for bud burst and flowering. Abscisic acid (ABA) levels were remarkably elevated in the dormant buds of both cultivars during endodormancy, but they were significantly higher in 'Honeycrisp' buds, especially during the transition from endo- to eco-dormancy. Through investigating ABA biosynthetic and catabolic genes, we identified two biosynthetic genes, NCED1 and NCED2 , and one catabolic gene CYP707A 2.3 , whose differential transcript levels can explain the distinctive ABA patterns in the two apple cultivars. Our data also showed higher cytokinin (CK) levels in the buds of 'Cripps Pink' compared to 'Honeycrisp', shortly before the time of budburst. The results of this study indicate that differences in bloom times among apple cultivars can be explained, at least partially, by the differential heat requirements and ABA levels during eco-dormancy. Future investigations, especially at the omics levels would provide better understanding of molecular networks linking ABA hemostasis with bud dormancy and bloom regulation in apple. [ABSTRACT FROM AUTHOR]