| Abiotic stresses such as salinity, drought and temperature extremes cause extensive loss to agricultural production worldwide. In order to further characterize plant responses to salinity, a proteomics-based investigation to identify and validate proteins whose levels were altered by salinity in pea ( Pisum sativum L.) roots was initiated. Several proteins including pathogenesis-related (PR) 10 proteins were identified using this approach. In order to test the hypothesis that PR 10 proteins play a crucial role in mediating plant responses to stress, we characterized transgenic Brassica napus and Arabidopsis thaliana plants expressing two different pea PR 10 cDNAs, PR 10.1 and ABR17 , respectively. Enhanced germination, early seedling growth and tolerance to abiotic stresses were observed in these transgenic plants. PR 10 proteins from various species have been demonstrated to be RNases, the RNase activity of pea PR 10 proteins was demonstrated by overexpressing the cDNAs of PR 10.1 and ABR17 in Escherichia coli and assaying for RNase activity. Since tRNA (and rRNA) can be sources of cytokinins (CKs) in plants, it was hypothesized that the PR 10-mediated effects were due to CK levels being modulated by the expression of PR 10 cDNAs in transgenic plants. Increased levels of CK in both transgenic B. napus and A. thaliana were observed which paralleled elevated expression of the primary CK-response regulator, ARR5, in A. thaliana. A role for the elevated CKs in mediating enhanced germination and early seedling growth of transgenic plants was confirmed by exogenous application of CK which increased germination and growth of wild type A. thaliana. Results presented in this study have demonstrated a crucial role for PR 10 genes in abiotic stress responses of plants. |
