Modulation of starch synthesis in Arabidopsis via phytochrome B-mediated light signal transduction

Starch is a major storage carbohydrate in plants and is critical in crop yield and quality.Starch synthesis is intricately regulated by internal metabolic processes and external environmental cues;however,the precise molecular mechanisms governing this process remain largely unknown.In this study,we revealed that high red to far-red(high R:FR)light significantly induces the synthesis of leaf starch and the expression of synthesis-related genes,whereas low R:FR light suppress these processes.Arabidopsis phytochrome B(phyB),the primary R and FR photoreceptor,was identified as a critical positive regulator in this process.Downstream of phyB,basic leucine zipper transcription factor ELONGATED HYPOCOTYL5(HY5)was found to enhance starch synthesis,whereas the basic helix-loop-helix transcription factors PHYTOCHROME INTERACTING FACTORs(PIF3,PIF4,and PIF5)inhibit starch synthesis in Arabidopsis leaves.Notably,HY5 and PIFs directly compete for binding to a shared G-box cis-element in the promoter region of genes encoding starch synthases GBSS,SS3,and SS4,which leads to antagonistic regulation of their expression and,consequently,starch synthesis.Our findings highlight the vital role of phyB in enhancing starch synthesis by stabilizing HY5 and facilitating PIFs degradation under high R:FR light conditions.Conversely,under low R:FR light,PIFs predominantly inhibit starch synthesis.This study provides insight into the physiological and molecular functions of phyB and its downstream transcription factors HY5 and PIFs in starch synthesis regulation,shedding light on the regulatory mechanism by which plants synchronize dynamic light signals with metabolic cues to module starch synthesis.

LeCDJ1,a chloroplast DnaJ protein,facilitates heat tolerance in transgenic tomatoes

The roles of a tomato （Lycopersicon esculentum） chloroplast-targeted DnaJ protein （LeCDJ1） were investigat-ed using wild-type （WT） and sense transgenic tomatoes. The LeCDJ1 expression was upregulated by 38℃, 42 ℃, 45 ℃, NaCl, PEG, methyl viologen （MV） and hydrogen peroxide （H2O2）, but not by 30 ℃ and 35 ℃. Meanwhile, LeCDJ1 was involved in the response of plants to abscisic acid （ABA）. Under heat stress, the sense plants showed better growth, higher chlorophyll content, lower malondialdehyde （MDA） accumulation and relative electrical conductivity （REC）, and also less PSII photoinhibition than WT. Interestingly, the sense plants treated with streptomycin （SM）, an inhibitor of organellar translation, still showed higher maximum photo-chemistry efficiency of PSII （Fv/Fm） and D1 protein levels than the SM-untreated WT, suggesting that the protective effect of LeCDJ1 on PSII was, at least partially, independent of D1＆amp;nbsp;protein synthesis. Furthermore, the relatively lower super-oxide radical （O2^＊-） and H2O2 levels in the sense plants were considered to be due to the higher ascorbate peroxidase （APX） and superoxide dismutase （SOD） activity, which seemed unlikely dependent on their transcription level. These results indicated that LeCDJ1 overexpression facilitated heat tolerance in transgenic tomatoes.

Regulation of Leaf Angle by Auricle Development n Maize

In plants, the leaf angle （LA） affects how densely crops can be planted and thus is one of factors determining grain yield per acre. This complex quantitative trait is controlled by developmental signals, hormones, and environmental factors （Luo et al., 2016）.

Phytochrome B interacts with LIGULELESS1 to control plant architecture and density tolerance in maize

Over the past few decades,significant improvements in maize yield have been largely attributed to increased plant density of upright hybrid varieties rather than increased yield per plant.However,dense planting triggers shade avoidance responses(SARs)that optimize light absorption but impair plant vigor and performance,limiting yield improvement through increasing plant density.In this study,we demonstrated that high-density-induced leaf angle narrowing and stem/stalk elongation are largely dependent on phytochrome B(phyB1/B2),the primaryphotoreceptor responsible for perceiving red(R)and far-red(FR)light in maize.We found that maize phyB physically interacts with the LIGULELESS1(LG1),a classical key regulator of leaf angle,to coordinately regulate plant architecture and density tolerance.The abundance of LG1 is significantly increased by phyB under high R:FR light(low density)but rapidly decreases under low R:FR light(high density),correlating with variations in leaf angle and plant height under various densities.In addition,we identified the homeobox transcription factor HB53 as a target co-repressed by both phyB and LG1 but rapidly induced by canopy shade.Genetic and cellular analyses showed that HB53 regulates plant architecture by controlling the elongation and division of ligular adaxial and abaxial cells.Taken together,these findings uncover the phyB-LG1-HB53 regulatory module as a key molecular mechanism governing plant architecture and density tolerance,providing potential genetic targets for breeding maize hybrid varieties suitable for high-density planting.

Histological and single-nucleus transcriptome analyses reveal the specialized functions of ligular sclerenchyma cells and key regulators of leaf angle in maize

Leaf angle(LA)is a crucial factor that affects planting density and yield in maize.However,the regulatory mechanisms underlying LA formation remain largely unknown.In this study,we performed a comparative histological analysis of the ligular region across various maize inbred lines and revealed that LA is significantly influenced by a two-step regulatory process involving initial cell elongation followed by subsequent lignification in the ligular adaxial sclerenchyma cells(SCs).Subsequently,we performed both bulk and single-nucleus RNA sequencing,generated a comprehensive transcriptomic atlas of the ligular region,and identified numerous genes enriched in the hypodermal cells that may influence their specialization into SCs.Furthermore,we functionally characterized two genes encoding atypical basic-helix-loop-helix(bHLH)transcription factors,bHLH30 and its homolog bHLH155,which are highly expressed in the elongated adaxial cells.Genetic analyses revealed that bHLH30 and bHLH155 positively regulate LA expansion,and molecular experiments demonstrated their ability to activate the transcription of genes involved in cell elongation and lignification of SCs.These findings highlight the specialized functions of ligular adaxial SCs in LA regulation by restricting further extension of ligular cells and enhancing mechanical strength.The transcriptomic atlas of the ligular region at single-nucleus resolution not only deepens our understanding of LA regulation but also enables identification of numerous potential targets for optimizing plant architecture in modern maize breeding.