Abstract
The light-harvesting chlorophyll a/b-binding (LHCB) proteins are the apoproteins of the light-harvesting complex of photosystem II. In the present study, we observed that downregulation of any of the six LHCB genes resulted in abscisic acid (ABA)-insensitive phenotypes in seed germination and post-germination growth, demonstrating that LHCB proteins are positively involved in these developmental processes in response to ABA. ABA was required for full expression of different LHCB members and physiologically high levels of ABA enhanced LHCB expression. The LHCB members were shown to be targets of an ABA-responsive WRKY-domain transcription factor, WRKY40, which represses LHCB expression to balance the positive function of the LHCBs in ABA signalling. These findings revealed that ABA is an inducer that fine-tunes LHCB expression at least partly through repressing the WRKY40 transcription repressor in stressful conditions in co-operation with light, which allows plants to adapt to environmental challenges.
Highlights
The light-harvesting chlorophyll a/b-binding (LHCB) proteins are the apoproteins of the light-harvesting complex of photosystem II (PSII)
We observed that abscisic acid (ABA) was required for full expression of different LHCB members and that physiologically high levels of ABA enhancedLHCB expression, and we have provided evidence to show that ABA functions through an ABA-responsive WRKY transcription factor, WRKY40, which represses LHCB expression to balance the function of the LHCB members in ABA signalling
We showed that the LHCB members positively regulate ABA signalling in seed germination and post-germination growth (Fig. 1)
Summary
The light-harvesting chlorophyll a/b-binding (LHCB) proteins are the apoproteins of the light-harvesting complex of photosystem II (PSII). We observed that the expression of all LHCB members except for LHCB4 was upregulated by 5 μM ABA treatment at both mRNA and protein levels when 6-d-old seedlings were transferred to ABA-containing MS medium for a period of 24 h (Supplementary Fig. S2 at JXB online.), which is essentially consistent with the observations of the 3-d-old plants grown for a longer time (2 weeks) in ABA-containing medium (Fig. 2A, C).
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