Abstract
Large and premature organ abscission may limit the industrial development of fruit crops by causing serious economic losses. It is well accepted that ethylene (ET) is a strong inducer of organ abscission in plants. However, the mechanisms underlying the control of organ abscission by ET are largely unknown. We previously revealed that LcKNAT1, a KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1)-like protein, acted as a negative regulator in control of fruitlet abscission through suppressing the expression of ET biosynthetic genes in litchi. In this study, we further reported that LcKNAT1 could also directly repress the transcription of LcEIL2 and LcEIL3, two ETHYLENE INSENSITIVE 3-like (EIL) homologs in litchi, which functioned as positive regulators in ET-activated fruitlet abscission by directly promoting the expression of genes responsible for ET biosynthesis and cell wall degradation. The expression level of LcKNAT1 was downregulated, while LcEIL2/3 was upregulated at the abscission zone (AZ) accompanying the fruitlet abscission in litchi. The results of electrophoretic mobility shift assays (EMSAs) and transient expression showed that LcKNAT1 could directly bind to the promoters of LcEIL2 and LcEIL3 and repress their expression. Furthermore, the genetic cross demonstrated that the β-glucuronidase (GUS) expression driven by the promoters of LcEIL2 or LcEIL3 at the floral AZ was obviously suppressed by LcKNAT1 under stable transformation in Arabidopsis. Taken together, our findings suggest that the LcKNAT1-LcEIL2/3 regulatory module is likely involved in the fruitlet abscission in litchi, and we propose that LcKNAT1 could suppress both ET biosynthesis and signaling to regulate litchi fruit abscission.
Highlights
Organ abscission is a widespread phenomenon throughout the life cycle of plants that occurs under stressful environmental conditions and as a result of its own developmental process (Sexton and Roberts, 1982; Patterson, 2001; Taylor and Whitelaw, 2001; Roberts et al, 2002; Estornell et al, 2013)
These results indicate that the expression pattern of LcEIL2/3 is opposite to that of LcKNAT1 during the fruitlet abscission process in litchi
We revealed that LcKNAT1 acts as a negative regulator of fruitlet abscission by repressing ET
Summary
Organ abscission is a widespread phenomenon throughout the life cycle of plants that occurs under stressful environmental conditions (biotic and abiotic) and as a result of its own developmental process (Sexton and Roberts, 1982; Patterson, 2001; Taylor and Whitelaw, 2001; Roberts et al, 2002; Estornell et al, 2013). The effect of ET on organ abscission is closely related to its biosynthesis and signal transduction pathway. As the core downstream transcription factor (TF) of ET signaling, ETHYLENE INSENSITIVE 3 (EIN3) and EIN3-LIKE (EIL) proteins are considered to play a crucial role in ETinduced organ abscission. ET treatment accelerated the leaf abscission of Chinese cabbage, in which the expression of BcEIL1/2/3 was significantly induced (Meng et al, 2019). We found that LcEIL2/3 functioned as positive regulators of fruitlet abscission in litchi, probably by activating the expression of genes responsible for ET biosynthesis and cell wall degradation (Ma et al, 2020). Previous studies strongly demonstrate that organ abscission is closely associated with ET biosynthesis and signaling. How the ACS/ACO genes are regulated and the mechanism underlying EIN3/EILs in the regulation of abscission remains elusive
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