دانلود رایگان مقاله انگلیسی فتوسنتز تقویت شده در ریشه های رشادی با فعالسازی عوامل رونوشتی GATA - اشپرینگر 2018

Abstract

Plant cells plastically change their functions according to the environment. Although Arabidopsis roots are heterotrophic organs, they increase photosynthetic capacity after shoot removal. Transcription factors regulating chloroplast development are involved in this response downstream of positive cytokinin and negative auxin regulation. To dissect the crosstalk of these regulators after shoot removal, we analyzed photosynthetic parameters in roots with chloroplast development enhanced by shoot removal, overexpression of transcription factors, or hormonal treatment. Our data suggest that shoot removal improves electron transfer downstream of PSII in roots, with a decrease in nonregulated energy dissipation. Cytokinin, auxin, and transcription factors affect the photosynthetic capacity of roots in a highly complex manner. Overexpression of two different types of transcription factors (GOLDEN 2-LIKE 1 and class-B GATAs) synergistically increased root chlorophyll content while maintaining high photosynthetic efficiency. Our data demonstrate the flexible regulation of the photosynthetic machinery by hormone signaling and downstream transcription factors.

Discussion

Rapid and transient ΦPSII development in detached roots is independent of cytokinin signaling:

We recently reported that shoot removal not only increases Chl content but also improves photosynthetic efficiency in Arabidopsis roots (Kobayashi et al. 2017). Image analysis of Chl fluorescence in roots revealed that shoot removal locally increased ΦPSII around the cut site near the root–hypocotyl junction, although intact wild-type roots showed more uniform ΦPSII levels from the basal to the middle areas (Fig. 1S). The data indicate that photosynthetic remodeling by shoot removal is a local response around the cut site. The data is consistent with the finding that chloroplast development is triggered by a local wounding response mediated by WINDs and type-B ARRs (Kobayashi et al. 2017). By contrast, ectopic overexpression of GNC and GNL increased ΦPSII over a wide area of the root, which suggests that GNC and GNL function to improve root photosynthesis at downstream of wounding and cytokininsignaling pathways. In detached roots, the cytokinin signaling around the wounding site may locally upregulate B-GATAs, particularly GNL, which subsequently induce chloroplast development and photosynthetic improvement around the cut site. Shoot removal greatly changes the induction kinetics of ΦPSII in wild-type roots, inducing transient ΦPSII development while rapidly suppressing ΦNO within a few minutes after actinic illumination. Type-B ARRs functioning downstream of cytokinin signaling, particularly ARR1 and ARR12, play a central role in the root greening response after shoot removal, upregulating transcription factors involved in chloroplast development, particularly GNL (Kobayashi et al. 2017), presumably in addition to directly inducing the expression of some photosynthesis-associated genes (Cortleven et al. 2016). However, although arr1 arr12 roots failed to accumulate Chl and increase steady-state ΦPSII level in response to shoot removal, they still showed a rapid and transient increase in ΦPSII on actinic illumination (Fig. 1A).