FLN2Interacts With FLN1to Regulate PEP-Dependent Plastid Gene Expression And Chloroplast Development In Arabidopsis

FLN1and FLN2belong to the pfkB family in plastid transcriptionallyactive chromosome (TAC). They are the targets of TRX z protein, whichregulates the PEP activity in Arabidopsis. Here, we investigated theT-DNA knockout lines of FLN2which displayed albino phenotype on MSmedium without sucrose, and decreased PEP-dependent plastid geneexpression. Transmission electron microscopy (TEM) analysis found thatthe chloroplast was highly vacuolated and lacked internal membranestructures. Yeast two-hybrid experiment showed that FLN2interacts withFLN1. Together with previous report that FLN1is important for PEP activityand chloroplast development, FLN2and FLN1might form a heterodimerto regulate PEP activity. The fln2-2mutants could gradually turn greenon sucrose-containing MS medium, and after transplanting the mutantswith the green leaves into soil, the mutants continued growing andcompleted their life cycles. However, the overall size of these mutantswas much smaller than that of the WT. Compared with another albinomutant trx z, we found that during the greening of the fln2-2mutantseedling, rbcL transcript can be specially accumulated, and its amountis close to that of wild type after two weeks. The transcript analysis ofPEP-dependent plastid genes suggested that PEP activity in fln2-2ishigher than that in trx z. This suggests that the specific accumulation ofrbcL and the PEP activity are critical for greening of fln2-2mutant.