UV-B Inhibits Leaf Growth through Changes in Growth Regulating Factors and Gibberellin Levels

Abstract

Ultraviolet-B (UV-B) radiation affects leaf growth in a wide range of species. In this work, we demonstrate that UV-B levels present in solar radiation inhibit maize (Zea mays) leaf growth without causing any other visible stress symptoms, including the accumulation of DNA damage. We conducted kinematic analyses of cell division and expansion to understand the impact of UV-B radiation on these cellular processes. Our results demonstrate that the decrease in leaf growth in UV-B-irradiated leaves is a consequence of a reduction in cell production and a shortened growth zone (GZ). To determine the molecular pathways involved in UV-B inhibition of leaf growth, we performed RNA sequencing on isolated GZ tissues of control and UV-B-exposed plants. Our results show a link between the observed leaf growth inhibition and the expression of specific cell cycle and developmental genes, including growth-regulating factors (GRFs) and transcripts for proteins participating in different hormone pathways. Interestingly, the decrease in the GZ size correlates with a decrease in the concentration of GA19, the immediate precursor of the active gibberellin, GA1, by UV-B in this zone, which is regulated, at least in part, by the expression of GRF1 and possibly other transcription factors of the GRF family.

Identification of peach growth regulating-factors and their expression under UVB

“…Therefore, we infer that the levels of GA 3 and IAA in the shoot tips inhibit the growth of the new shoot to a certain extent, and thus regulate tree potential. Studies in maize indicate that the inhibitory effect of UVBs on growth is mediated by GRF, some of which might be regulated by miR396, thereby modifying GA levels in the leaf growth zone [29,30,56]. To further verify the above hypothesis, we tested the expression of miR396.…”

“…There is much evidence indicating the role of GRFs in various biological processes through interacting with different clients, such as hormone pathways, stomatal behavior, reactive oxygen species balance, and ion transport [61][62][63][64][65]. In Arabidopsis and maize, UVB radiation inhibits leaf growth by decreasing the expression of GRFs [29,30,56]. This ultimately leads to a reduced expression of GA biosynthetic genes and increased levels of catabolic transcripts [26,29,30,56].…”

“…MiR396 expression is caused by various abiotic stresses, such as high salinity, low temperature, drought stress, and UVB. Several reports indicate that UVB leaf growth inhibition requires GRF1 activity, while miR396/GRF exerts it has an in uence on organ growth by regulating (at least partially) the expression of GA metabolic genes [25,[27][28][29].…”

“…UVB radiation treatment of Arabidopsis causes the accumulation of DNA damage and limits leaf expansion by inhibiting cell division in proliferating tissues [30]. Reduced maize leaf growth under UVB irradiation is the result of reduced cell production and a shortened growth zone [29]. This inhibition is regulated, at least in part, by transcription factors of the GRF family, some of which are probably regulated by miR396, which modi es GA levels [29].…”

“…Reduced maize leaf growth under UVB irradiation is the result of reduced cell production and a shortened growth zone [29]. This inhibition is regulated, at least in part, by transcription factors of the GRF family, some of which are probably regulated by miR396, which modi es GA levels [29]. Soybean plant morphology is substantially altered in response to shade stress.…”