Repression of drought-induced cysteine-protease genes alters barley leaf structure and responses to abiotic and biotic stresses

Abstract

To survive under water deficiency, plants alter gene expression patterns, make structural and physiological adjustments, and optimize the use of water. Rapid degradation and turnover of proteins is required for effective nutrient recycling. Here, we examined the transcriptional responses of the C1A cysteine protease family to drought in barley and found that four genes were up-regulated in stressed plants. Knock-down lines for the protease-encoding genes HvPap-1 and HvPap-19 showed unexpected changes in leaf cuticle thickness and stomatal pore area. The efficiency of photosystem II and the total amount of proteins were almost unaltered in stressed transgenic plants while both parameters decreased in stressed wild-type plants. Although the patterns of proteolytic activities in the knock-down lines did not change, the amino acid accumulation increased in response to drought, concomitant with a higher ABA content. Whilst jasmonic acid (JA) and JA-Ile concentrations increased in stressed leaves of the wild-type and the HvPap-1 knock-down lines, their levels were lower in the HvPap-19 knock-down lines, suggesting the involvement of a specific hormone interaction in the process. Our data indicate that the changes in leaf cuticle thickness and stomatal pore area had advantageous effects on leaf defense against fungal infection and mite feeding mediated by Magnaporthe oryzae and Tetranychus urticae, respectively.

Plant Defenses Against Tetranychus urticae: Mind the Gaps

“…For instance, an increased leaf trichome density in raspberry (Rubus idaeus L.) correlated negatively with spider mite presence and demonstrated that this antixenosis trait hampered the spider mite movement and limited the mite egg deposition [29]. Gomez-Sanchez et al [30] have recently shown that the thicker leaf cuticles detected in barley (Hordeum vulgare) HvPap-1 knockdown plants protected leaves from T. urticae feeding probably by hindering stylet penetration into the leaf mesophyll.…”

Plant Proteases: From Key Enzymes in Germination to Allies for Fighting Human Gluten-Related Disorders

“…Plant proteases have been described to accomplish multiple roles in different physiological processes along the plant life cycle, such as programmed cell death, senescence, abscission, fruit ripening, plant growth, and N homeostasis (Grudkowska and Zagdańska, 2004; van der Hoorn, 2008; Liu et al, 2018; Tornkvist et al, 2019). In response to abiotic and biotic stresses, proteases are also involved in nutrient remobilization associated with leaf and root proteins degradation to ensure yield (Diaz-Mendoza et al, 2014; Velasco-Arroyo et al, 2016, 2018; Gomez-Sanchez et al, 2019; James et al, 2019), or in triggering the response of the plant to pathogens and phytophagous insects and acari (van der Hoorn and Jones, 2004; Shindo and van der Hoorn, 2008; Misas-Villamil et al, 2016; Diaz-Mendoza et al, 2017). Moreover, plant proteases play a crucial role in the plant seed germination, through the mobilization of other proteins accumulated in seeds and cereal grains (Grudkowska and Zagdańska, 2004; Cambra et al, 2012; Diaz-Mendoza et al, 2016; Szewinska et al, 2016; Liu et al, 2018; Radchuk et al, 2018).…”

Plant proteases and programmed cell death

“…Many C1A cysteine proteases, including the cathepsins, have typically been associated with nutrient recycling. Gomez-Sanchez et al (2019) found four genes to be up-regulated in barley leaves upon drought stress. Knock-down lines for two of these genes, HvPap-1 and HvPap-19 , led to changes in leaf cuticle thickness and stomatal pore area, and photosystem efficiency and protein homeostasis were much less affected than in drought-stressed wild-type plants.…”

“…Knock-down lines for two of these genes, HvPap-1 and HvPap-19 , led to changes in leaf cuticle thickness and stomatal pore area, and photosystem efficiency and protein homeostasis were much less affected than in drought-stressed wild-type plants. Unexpectedly, stress hormone levels were altered and the changes in cuticle thickness and stomatal pore area had advantageous effects on leaf defense against fungi and mites (Gomez-Sanchez et al , 2019).…”