The 14-3-3 protein binds to the nuclear matrix endonuclease and has a possible function in the control of plant senescence

The nuclear matrices of plant cell nuclei display an intrinsic nuclease activity which is capable of nicking supercoiled DNA. Recently a cDNA encoding the 14-3-3 protein from Cucurbita pepo has been cloned and sequenced. The evidence that the recombinant 14-3-3 protein associates with DNase I and endogenous plant nuclease is presented. Evidence is also presented that the cloned 14-3-3 protein isoform, unique in its binding to nuclease within the 14-3-3 family, is located in the nuclei and in the nuclear matrix. Transgenic potato plants were created where the 14-3-3 protein derived from Cucurbita was overexpressed. An increase in tuber number and a decrease in tuber size in the transformants was also observed. The adenine nucleotide pool in leaves of transgenic plants was significantly reduced and they contain more chlorophyll and loose it slower when grown in the dark. A decrease in 14-3-3 protein content concomitant with an increase in nuclease activity in senescent plants was detected and this was markedly delayed in transgenic potato plants which overexpressed the 14-3-3 protein. It is proposed that a function of the isolated 14-3-3 isoform is the control of the nuclease activity and hence senescence.