Plant hormones (Literature sources on phytohormones and plant signalling)

Journal of Experimental Botany (2023)

Abstract: "In nature, plant shoots are exposed to light whereas the roots grow in relative darkness. Surprisingly, many root studies rely on in vitro systems that leave the roots exposed to light whilst ignoring the possible effects of this light on root development. Here, we investigated how direct root illumination affects root growth and development in Arabidopsis and tomato. Our results show that in light-grown Arabidopsis roots activation of local phytochrome A and B by far-red or red light inhibits respectively PHYTOCHROME INTERACTING FACTORs 1 or 4, resulting in decreased YUCCA4 and YUCCA6 expression. As a result, auxin levels in the root apex become suboptimal, ultimately resulting in reduced growth of light-grown roots. These findings highlight once more the importance of using in vitro systems where roots are grown in darkness, for studies that focus on root system architecture. Moreover, we show that the response and components of this mechanism are conserved in tomato roots, thus signifying its importance for horticulture as well. Our findings open up new research possibilities to investigate the importance of light-induced root growth inhibition for plant development, possibly by exploring putative correlations with responses to other abiotic signals, such as temperature, gravity, touch, or salt stress."

Authors: Jianyu Zhao, Kailiang Bo, Yupeng Pan, Yuhong Li, Daoliang Yu, Chuang Li, Jiang Chang, Shuang Wu, Zhongyi Wang, Xiaolan Zhang, Xingfang Gu and Yiqun Weng.

Journal of Experimental Botany (2023)

Highlight: Cucumber phytochrome interacting factor 3 (CsPIF3) physically interacts with both CsPhyB and CsUVR8 connecting the red/far-red and UVB light response pathways for hypocotyl growth.

Abstract: "In Arabidopsis, the photoreceptors phytochrome B- (PhyB) and UVB resistance 8- (UVR8) mediated light responses play a major role in regulating photomorphogenic hypocotyl growth, but how they crosstalk to coordinate this process is not well understood. Here we report map-based cloning and functional characterization of a UVB-insensitive, long-hypocotyl mutant, lh1, and a wild-type-like lh2 mutant in cucumber, Cucumis sativus, which encodes a defective CsPhyB and a key gibberellic acid (GA) biosynthesis enzyme CsGA20ox-2, respectively. The lh2 mutation was epistatic to lh1 and partly suppressed long-hypocotyl phenotype in the lhl1lh2 double mutant. We identified phytochrome interacting factor (PIF) CsPIF3 that played a critical role in integrating the red/far-red and UVB light responses for hypocotyl growth. We show that two modules, CsPhyB-CsPIF3-CsGA20ox-2 (GA oxidase2)-DELLA and CsPIF3-CsARF18 (auxin response factor 18) mediate CsPhyB-regulated hypocotyl elongation through GA and auxin pathways, respectively, in which CsPIF3 binds to the G-/E-box motifs in the promoters of CsGA20ox-2 and CsARF18 to regulate their expression. We also identified a new physical interaction between CsPIF3 and CsUVR8 mediating CsPhyB-dependent, UVB-induced hypocotyl growth inhibition. Our work suggests that hypocotyl growth in cucumber involves a complex interplay of multiple photoreceptor- and phytohormone-mediated signaling pathways that show both conservation with and divergence from those in Arabidopsis."

Author: Humberto Herrera-Ubaldo