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Fruit abscission is a severe hindrance to commercial crop production, and a lack of carbohydrates causes fruit abscission to intensify in a variety of plant species. However, the precise mechanism by which carbohydrates affect fruit setting potential has yet to be determined. In the current study, we noticed negative correlation between hexose level and fruit setting by comparing different cultivars, bearing shoots of varying diameters, and girdling and defoliation treatments. The cumulative fruit-dropping rate was significantly reduced in response to exogenous glucose dipping. These results suggested that hexose, especially glucose, is the key player in lowering litchi fruit abscission. Moreover, five putative litchi hexokinase genes (LcHXKs) were isolated and the subcellular localization as well as activity of their expressed proteins in catalyzing hexose phosphorylation were investigated. LcHXK2 was only found in mitochondria and expressed catalytic protein, whereas the other four HXKs were found in both mitochondria and nuclei and had no activity in catalyzing hexose phosphorylation. LcHXK1 and LcHXK4 were found in the same cluster as previously reported hexose sensors AtHXK1 and MdHXK1. Furthermore, VIGS-mediated silencing assay confirms that LcHXK1 suppression increases fruit abscission. These findings revealed that LcHXK1 functions as hexose sensor, negatively regulating litchi fruit abscission. [ABSTRACT FROM AUTHOR]

Wild banana species are essential natural gene pools for banana improvement. In this study, six RGAs about 500 bp were obtained from leaves of Musa acuminata, a wild banana shown to be resistant to banana Fusarium wilt race 4, by PCR amplification with degenerate primers designed according to the conserved NBS motif and serine/threonine kinase domain of plant resistance (R) genes. Among these RGAs, the deduced amino acids of WNB1 and WNB2 contain NB-ARC domain and WNB1 can be translated into polypeptide uninterrupted by stop codons. The deduced amino acids of other four RGAs (WST1, WST2, WST3 and WST4) all contain the serine/threonine kinase domain and WST3 encodes a polypeptide homologous to that of bacterial blight resistance gene Xa21 of rice. At different time after inoculation with Fusarium oxysporum f. sp. cubense (FOC) race 4, the transcript patterns of WNB1 and WST3 was enhanced, which implied that the expression of WNB1 and WST3 may be related to the resistance of banana to Fusarium wilt.