Fighting for the light: how plants deal with nearby vegetation

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Fighting for the light: how plants deal with nearby vegetation

An article recently published in The Plant Cell shows that differences in phytocrome A photoreceptors determine the plant strategy to the proximity of other plants.
Drawing of Arabidopsis seedlings under SAS (Credit: Swasky)
Drawing of Arabidopsis seedlings under SAS (Credit: Swasky)

Plant growth is highly dependent on the availability and quality of light, which is the source of energy used for the photosynthesis. In both natural habitats and crop fields, plants are surrounded by vegetation with which they compete for the light. A work led by the ICREA researcher at CRAG Jaume Martínez-García recently published in The Plant Cell, compared the differences in response to the shade produced by nearby vegetation, known as Shade Avoidance Syndrome (SAS), between two closely related plant species, Arabidopsis thaliana and Cardamine hirsute. They focused in the hypocotyl elongation and, by using a genetic approach, they showed that photoreceptors are key players in the different strategies these plants implement to adapt to SAS.

Different responses to the shade

Some plants try to escape to the proximity to other plants (sensed by the shade or the change in the light quality) by strongly elongating. These are the so-called shade-avoiding species, and some of the main responses to this proximity are the hypocotyl elongation (to overgrow the neighbouring plants and reach the light), the induction of the flowering (to ensure a next generation) and the adjustment of the photosynthesis rates by a reduction in the levels photosynthetic pigments. On the other hand, some plants are tolerant to this proximity and do not show any elongation response. The CRAG team wondered how different plant species adopt opposite strategies to respond to the same environmental challenge.

Even though Arabidopsis thaliana and Cardamine hirsuta are close relative species, C. hirsuta is shade-tolerant, while A. thaliana undergoes an avoidance response to shade. To determine the cause of this difference, authors performed a genetic screening using an EMS-mutagenized population of C. hirsuta, looking for seedlings that strongly elongate the hypocotyls under simulated shade. The researchers identified two mutants, which they named slender in shade 1 (sis1). The molecular analysis of the identified mutants revealed that the sis1 mutants lacked the phytochrome A (PhyA) photoreceptor protein. This is consistent with the fact that wild-type Arabidopsis plants, which respond to the shade, have lower levels of PhyA than C. hirsuta, and phenotypically present a very similar pattern of response. 

In conclusion, the authors were able to show that the phytocrome A is responsible, at least in part, for the differences in the hypocotyl elongation in both species in response to shade.

The importance of understanding SAS  

The study lead by Martínez-García reveals the potential of modulating photoreceptor activity as a powerful evolutionary mechanism in nature to achieve physiological variation between species and enabling the colonization of new, different habitats. 

Several agricultural applications can derive from the knowledge generated in this work. Generation of shade-tolerant crop varieties able to grow well at high planting density could maximize land use and productivity. In addition, engineering shade-avoiding beneficial weeds (i.e., those that can provide refuge to beneficial animals and insects or enhance soil quality) can allow them to grow in shaded or semi-shaded areas to be used in Conservation Agriculture approaches.

 

Reference article

Maria Jose Molina-Contreras, Sandi Paulišić, Christiane Then, Jordi Moreno-Romero, Pedro Pastor-Andreu, Luca Morelli, Irma Roig-Villanova, Huw Jenkins, Asis Hallab, Xiangchao Gan, Aurelio Gomez-Cadenas, Miltos Tsiantis, Manuel Rodríguez-Concepción and Jaime F. Martínez-García. Photoreceptor activity contributes to contrasting responses to shade in Cardamine and Arabidopsis seedlings. The Plant Cell, 31: 2649–2663 (2019). Doi: 10.1105/tpc.19.00275