Sorbitol in loquat promotes early flower bud differentiation via the MADS-box transcription factor EjCAL

The sugar alcohol sorbitol plays an important signaling role in fruit trees. Here, we found that sorbitol significantly increased during flower bud differentiation (FBD) in loquat (Eriobotrya japonica Lindl.) from the physiological FBD stage (EjS1) to the morphological FBD stage (EjS2), and it then decreased in the panicle development stage (EjS3) compared to in EjS2, and in subsequent stages. Spraying sorbitol increased the sorbitol content and thereby promoted early FBD and increased the proportion of flower buds that completed FBD. A transcriptomics analysis showed that the expression of a MADS-box transcription factor (TF) family gene, EjCAL, was highly correlated with the FBD phenotypic data. EjCAL-overexpressing transgenic tobacco exhibited the early FBD phenotype. Using the EjCAL promoter as bait in a yeast-one hybrid (Y1H) assay, the TF ERF12 was identified. Chromatin immunoprecipitation (ChIP)-PCR confirmed that EjERF12 can bind to the EjCAL promoter, and β-glucuronidase (GUS) activity assays demonstrated that EjERF12 can regulate EjCAL expression. Spraying loquat with sorbitol confirmed that EjERF12 and EjCAL expression were regulated by sorbitol. We also identified downstream functional genes (EjUF3GaT1, EjGEF2, and EjADF1) that might be involved in FBD. Finally, we found that the change in the level of hyperoside (a reproduction-related flavonoid) was consistent with that of sorbitol during FBD in loquat, and EjCAL can bind to the EjUF3GaT1 promoter and might thereby regulate hyperoside biosynthesis. Two early- and late-flowering varieties of loquat and EjCAL-overexpressing transgenic tobacco plants were used to confirm this hypothesis.One-sentence summarySorbitol promotes bud differentiation via EjCAL.

Allocation of Photoassimilates in Bud and Fruit from Different Leaf Nodes of Camellia oleifera

The periods of flower bud differentiation and fruit growth for Camellia oleifera overlap greatly affect the allocation of photoassimilates to flower buds and fruit, resulting in obvious alternate bearing. To export the cause and mitigate alternate bearing of Camellia oleifera, the allocation of photoassimilates to buds and fruit supplied by leaves at different node positions was studied by the addition of labeled 13CO2 during the slow fruit growth stage. The fate of 13C photoassimilated carbon was followed during four periods: slow fruit growth (4 hours and 10 days after 13C labeling); rapid growth (63 days after 13C labeling); oil conversion (129 days after 13C labeling); and maturation (159 days after 13C labeling). Photosynthetic parameters and leaf areas of the leaves shared a common pattern (fifth > third > first), and the order of photosynthetic parameters of different fruit growth stages was as follows: oil conversion > maturation > rapid growth > slow growth. The most intense competition between flower bud differentiation and fruit growth occurred during the oil conversion stage. Dry matter accumulation in different sinks occurred as follow: fruit > flower bud > leaf bud. Photoassimilates from the labeled first leaf were mainly translocated to the first flower bud, and the upper buds were always differentiated into flower buds. The photoassimilates from the labeled third leaf were distributed disproportionately to the third flower bud and fruit. They distributed more to the third flower bud, and the middle buds formed either flower or leaf buds. However, the photoassimilates from the labeled fifth leaf were primarily allocated to the fruit that bore on the first node of last year’s bearing shoot, and basal buds did not form flower buds. Based on our results, the basal leaves should be retained for a high yield in the current year, and the top leaves should be retained for a high yield in the following year. Our results have important implications for understanding the management of flower and fruit in C. oleifera. The thinning of fruit during the on-crop year can promote flower bud formation and increase the yield of C. oleifera crops in the following year. During the off-year, more fruit should be retained to maintain the fruit yield. The thinning of middle-upper buds could promote more photoassimilates allocate to the fruit.

Comprehensive Identification and Expression Analysis of the Members of the B-Box Gene Family of Cotton Involved in Flower bud Differentiation and Responses to Multiple Stresses

Background: B-BOX (BBX) proteins are zinc-finger transcription factors with one or two BBX domains and sometimes a CCT domain. These proteins play an essential role in regulating plant growth and development, as well as in resisting abiotic stress. So far, the BBX gene family has been widely studied in other crops. However, no one has systematically studied the BBX gene in cotton. Results: In the present study, 17, 18, 37 and 33 BBX genes were detected in Gossypium arboreum, G. raimondii, G. hirsutum and G. barbadense, respectively, via genome-wide identification. Phylogenetic analysis showed that all BBX genes were divided into 5 main categories. The protein motifs and exon/intron structures indicated that each group of BBX genes was highly conserved. Collinearity analysis revealed that the amplification of BBX gene family in Gossypium spp. was mainly through segmental replication. Nonsynonymous (Ka)/ synonymous (Ks) substitution ratios indicated that the BBX gene family had undergone purification selection throughout the long-term natural selection process. Moreover, transcriptomic data showed that some GhBBX genes were highly expressed in floral organs. Transcriptome data analysis and qRT-PCR verification showed that different GhBBX genes had different biological functions in flower bud differentiation, abiotic stress and stress response. Conclusions: Our comprehensive analysis of BBX in G. hirsutum provides a basis for further study on the molecular role of GhBBXs in regulating flowering and cotton resistance to abiotic stress.

Effects of carbon, nitrogen, phosphorus, and potassium on flowering and Fruiting of Glycyrrhiza uralensis

Carbon (C), nitrogen (N), phosphorus (P), and potassium (K) play an important role in flower bud differentiation and seed-filling; however, the effects of these elements on the flowering and fruiting of Glycyrrhiza uralensis Fisch. are not known. In this study, we evaluated the differences in the C, N, P, and K levels between the fruiting and nonfruiting plants of G. uralensis at different growth stages. The correlations between the elements C, N, P, and K and the flower and fruit falling rates, rate of empty seeds, rate of shrunken grains, and thousand kernel weight (TKW) were also determined. The results show that the P and K levels and C:N, P:N, and K:N ratios of flowering plants are significantly higher than those of nonflowering plants; N level of flowering plants is significantly lower than that of nonflowering plants at the flower bud differentiation stage. The number of inflorescences was positively correlated with C and K levels and C:N and K:N ratios. A low level of C, P, and K and high level of N in flowering and pod setting stage may lead to the flower and fruit drop of G. uralensis. The K level is significantly negatively correlated with the rates of empty and shrunken seeds. The N level is significantly positively correlated with TKW. Thus, high levels of C, P, and K might be beneficial to flower bud differentiation, while higher levels of N is not beneficial to the flower bud formation of G. uralensis. Higher levels of N and K at the filling stage were beneficial to the seed setting and seed-filling of G. uralensis.HighlightHigh levels of C, P, and K might be beneficial to flower bud differentiation, while higher levels of N is not beneficial to the flower bud formation of G. uralensis. Higher levels of N and K at the filling stage were beneficial to the seed setting and seed-filling of G. uralensis.

Variation of Endogenous Hormones during Flower and Leaf Buds Development in ‘Tianhong 2’ Apple

Hormones have an important role in apple flower bud differentiation; therefore, it is necessary to systematically explore the dynamic changes of endogenous hormones during flower and leaf bud development to elucidate the potential hormone regulation mechanism. In this study, we first observed the buds of ‘Tianhong 2’ apple during their differentiation stage using an anatomical method and divided them into physiologically differentiated stages of spur terminal buds, flower buds, and leaf buds. Then, we determined the contents of zeatin riboside (ZR), abscisic acid (ABA), auxin (IAA), and gibberellin (GA3) in these various types of buds using an enzyme-linked immunosorbent assay. The results showed that the content of ZR and the ratio of ZR to IAA in spur terminal buds decreased significantly during physiological differentiation. The contents of ZR, IAA, and GA3 in leaf buds culminated at the initial differentiation stage. The content of ZR in flower buds was significantly higher than that in leaf buds after formation of the inflorescence primordium and sepal primordium. Before the appearance of stamen primordium, the content of GA3 in flower buds was remarkably lower than that in leaf buds. The ratios of ABA/IAA and ZR/IAA in flower buds were significantly higher than those in leaf buds before the appearance of flower organ primordium. Moreover, ABA content, ABA/ZR, and ABA/GA3 in flower buds were higher than those in leaf buds throughout the whole flower bud morphological differentiation process. Therefore, the reduced ZR content was beneficial to floral induction. The low content of GA3, and high ratios of ABA/IAA and ZR/IAA were conducive to early morphological differentiation. In addition, high ratios of ABA/GA3 and ABA/ZR were beneficial to the morphological differentiation of flower buds. Moreover, the high ABA content was beneficial to floral induction and morphological differentiation of flower buds. Our results shed light on the mechanisms of hormonal regulation of apple flower bud differentiation and could potentially strengthen the theoretical basis for artificial regulation of apple flower bud development using exogenous plant hormones.