The balance between growth and resistance is shifted to the latter by overaccumulation of chloroplast-nucleus located WHIRLY1 in barley

Abstract

WHIRLY1 is a chloroplast-nucleus located DNA/RNA-binding protein with functions in development and stress tolerance. By overexpression of HvWHIRLY1 in barley, lines with a 10-and two lines with a 50-fold accumulation of the protein were obtained. In these lines, the relative abundance of the nuclear form exceeded that of the chloroplast form indicating that over-accumulating WHIRLY1 exceeded the amount that chloroplasts can sequester. Growth of the plants was shown to be compromised in a WHIRLY1 abundance-dependent manner. Over-accumulation of WHIRLY1 in chloroplasts had neither an evident impact on nucleoid morphology nor on the composition of the photosynthetic apparatus. Nevertheless, oeW1 plants were found to be compromised in the efficiency of photosynthesis. The reduction in growth and photosynthesis was shown to be accompanied by a decrease in the levels of cytokinins and an increase in the level of jasmonic acid. Gene expression analyses revealed that already in non-stress conditions the oeW1 plants had enhanced levels of pathogen response (PR) gene expression indicating activation of constitutive defense. During growth in continuous light of high irradiance, PR1 expression further increased in addition to an increase in the expression of PR10 and of the gene encoding phenylalanine lyase (PAL), the key enzyme of salicylic acid biosynthesis in barley. The activation of defense gene expression in oeW1 plants coincided with an enhanced resistance towards powdery mildew, which in barley is independent of salicylic acid. Taken together, the results show that over-accumulation of WHIRLY1 in barley to levels of 10 or more, amplified the tradeoff between growth and stress resistance.