![kami blue github kami blue github](https://64.media.tumblr.com/a355d2fce8b38756c9e79b39db2ad077/tumblr_olemc2Ckbl1tgq989o1_1280.jpg)
NPH3 and RPT2 can physically interact with phot1 and each other ( 16, 18). Phot1, NPH3, and RPT2 all are associated with the plasma membrane, particularly in elongating cells ( 16, 20). nph3 null mutants show no phototropic curvature at any blue light fluence rates, whereas the rpt2 mutant is impaired in phototropism only at high fluence rates ( 17, 18). They belong to a plant-specific family of proteins possessing a BTB/POZ (broad complex, tramtrack, bric à brac/pox virus, and zinc finger) and a coiled-coil domain, both thought to be involved in protein–protein interaction ( 16).
![kami blue github kami blue github](https://user-images.githubusercontent.com/29214314/97220413-6f51d080-1799-11eb-8bc0-0b7ebfb0bd93.png)
NONPHOTOTROPIC HYPOCOTYL 3 (NPH3) and ROOT PHOTOTROPISM 2 (RPT2) function as signal transducers in phototropism signaling ( 16 – 19). Light triggers a conformational change in the photoreceptor that activates its protein kinase activity, but very few specific phototropism signaling components have been identified ( 2, 14, 15). Phototropin-mediated responses are thus particularly important for normal plant growth under extreme (very low or very high) light conditions ( 11 – 13).ĭespite the obvious importance of phototropism, the signaling mechanisms operating downstream of light perception are poorly understood.
![kami blue github kami blue github](https://cdn.discordapp.com/attachments/780094001331961901/796061357858488450/2021-01-05_17.57.23.png)
Together, these responses all are believed to maximize photosynthetic light capture while minimizing photodamage ( 8, 10). Phot1 and phot2 are not only required for phototropism but also for chloroplast movement, stomatal opening, and leaf flattening. Phot1 is necessary and sufficient under a weak source of blue light, whereas phot1 and phot2 act redundantly to mediate phototropism under high blue light ( 9). Light direction is perceived by the phototropin family of UV-A/blue light sensors ( 2, 8). Under low fluence rates of blue light, phytochrome A (phyA) is the predominant photoreceptor that triggers repression of gravitropism ( 6, 7). But as soon as the seedlings perceive a weak source of light, even under the soil, gravitropism is repressed and phototropism predominates ( 3 – 5). Arabidopsis thaliana hypocotyls use gravity in darkness to orient their growth in the soil. These processes are called gravitropism and phototropism ( 1 – 3). They determine their direction of growth by sensing and responding to the gravity vector and the direction of light. Plants need to reach the light and start photosynthesis before the seed reserves have been exhausted. Plants’ survival depends on their ability to orient growth appropriately at the very beginning of their development. We show that PKS1 induction by a pulse of blue light is phytochrome A-dependent, suggesting that the PKS proteins may provide a molecular link between these two photoreceptor families. The phytochromes are known to influence phototropism but the mechanism involved is still unclear.
![kami blue github kami blue github](https://iwbry.kunstinlewenborg.nl/templates/64af9ff6ec07d70d68e9adf4e68843a5/img/0d96fda59036b686f7a97041cace212b.jpg)
Furthermore, PKS1 interacts with phot1 and NPH3 in vivo at the plasma membrane and in vitro, indicating that the PKS proteins may function directly with phot1 and NPH3 to mediate phototropism. Photobiological experiments show that the PKS proteins are critical for hypocotyl phototropism. The strong enhancement of PKS1 expression by blue light and its light induction in the elongation zone of the hypocotyl prompted us to study the function of this gene family during phototropism. PHYTOCHROME KINASE SUBSTRATE (PKS) 1 and PKS2 are two phytochrome signaling components belonging to a small gene family in Arabidopsis ( PKS1– PKS4). Only NONPHOTOTROPIC HYPOCOTYL 3 (NPH3) and root phototropism 2, both belonging to the same family of proteins, have been previously identified as phototropin-interacting signal transducers involved in phototropism. Lateral differences in low fluence rates of blue light are detected by phototropin 1 (phot1) in Arabidopsis. Phototropism, or plant growth in response to unidirectional light, is an adaptive response of crucial importance.